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Volume 63, 1934
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A Microscopical Study of the Structure of the Leaves of the Genus Pinus.

[Received by Editor in revised form, 19th January, 1933; issued separately, January, 1934.]

The introduction and propagation of many species of exotic conifers have been proceeding in New Zealand for approximately eighty years, and there now exist throughout the Dominion specimen trees of different ages as well as many specimens which exhibit individually characteristic growth or display forms varying from the type, thus rendering unreliable their identification from macroscopical characters.

At the instigation of Mr A. Hansson, Chief Inspector of Forestry, this study was carried out during 1929 to ascertain the possibilities of analysing the microscopic characters of leaves of various species of the genus Pinus in such a way as to form a key which could be used to verify the identification of the species by macroscopic characters. In many cases the latter differ within a species with variation of site and growing conditions, age, etc., hence identification by such factors may not be conclusive. It is at this stage that the examination of the microscopic characters of the leaves may furnish discriminatory evidence enabling a conclusion to be arrived at.

With this object in view, as many species as were available from different localities in New Zealand were examined, and their characters were then analysed to produce the appended key embodying diagnostic characters of forty species. Any conclusions arrived at to date must be considered as preliminary only, as variation of habitat, origin of the type, etc., may be found, on subsequent examination of a greater diversity of specimens, to affect the structure, and hence the diagnostic characters assigned in this table. The species included in the study are designated according to the names by which the original specimens were known in the Forest Service nurseries.

Technical Procedure.

The cross section from the middle of an average needle was used as the basis of examination, and wherever any indication arose of variation in structure, sections were cut at different positions along the length of the needle in order to counterbalance differences found to be due to rearrangement of tissues near the tips or bases of the leaf.

Sectioning was at first carried out freehand, using a razor with a blade flat on one side and cutting into material mounted as a bundle of several leaves tied tightly together.

Satisfactory sectioning was carried on by this means, but an attempt was then made to reduce the time spent on tool sharpening by adopting the use of safety razor blades mounted in a patent

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holder. This form of microtome knife was constructed by the Chief Inspector, and was used at first for hand cutting, in conjunction with a hand microtome, but by a little adjustment it was made to fit into a Bausch and Lomb swinging microtome, and was used thus for most of the sectioning work.

The material was mounted for cutting in a paraffin wax block by placing three or four short lengths of the needle upright in some warm wax poured into the cavity of a brass hand microtome, and then filling to the top with melted wax (the wax was found to cut most smoothly and easily when it had been kept below a temperature of 80° F. while melting, and was used soon after being cooled). The block could then be screwed up out of the holder and trimmed to fit into the microtome. Great difficulty was experienced in preventing the wax shavings from curling up as the cut was made, but it was found absolutely necessary to prevent this, as the sections mounted in curled wax almost invariably emerged with broken tissues. The most satisfactory method found was to keep the melting temperature of the wax low, and to have the material as soft and wet as possible.

Material.

Wherever available, freshly collected material was preferred for sectioning, but where this was not available it was found to be most satisfactory to cut needles into short lengths and leave them immersed in fresh water in a stoppered test tube until required for cutting. In the case of hard needles, glycerine added to the water (about 1 in 20) helped to soften them for cutting.

It is much more difficult to cut thin and perfect sections from needles of certain species than from others. This is due to the presence or to the arrangement of the schlerozed cells just below the epidermis, which in some instances serve to turn the fine blade-edge of the cutter, while in other cases the thin-walled cells between groups of hypodermal sclerenchyma are not strong enough to hold the tissues together when cut into very thin sections, and difficulty is experienced in obtaining a perfectly whole section by the end of the mounting process.

Preparation of Slides.

It was found necessary to stain sections in order to show up the structure for photography. For this purpose, fuchsin or saffranin were found to be most satisfactory as a cell-wall stain, the former acting on lignified tissue, and to a certain extent also on cellulose walls, while saffranin stained both lignified and cellulose walls together with certain cell contents. To differentiate the cells of the mesophyll from those of resin ducts in the cases where the latter were not sclerozed (lignified), eosin was found to be a good agent, although this stain was not satisfactory as a tissue stain.

The following procedure was adopted for preparation of the sections, and was varied, according to the type of material, in such details as the times necessary for each treatment or by the exclusion of certain steps in the process.

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Fresh material was cut from water and was kept wet by continual moistening whilst being cut. Sections were then placed in 50% (approximately) alcohol for a minute and transferred into either absolute alcohol or methylated spirits and left until all the green colouring matter was extracted—a matter of a half to several hours according to the material. The sections were then transferred into a 1 ½ inch watch glass containing a drop of staining solution in the glass full of water. If sections were of a fragile nature they were taken back through 50% alcohol into the stain. The time of staining varied from fifteen minutes to one hour, and sections were then passed through 50% alcohol again into absolute alcohol to rinse out excess of stain. If necessary, a second absolute alcohol rinsing was given. The stained material was then placed into clove oil for about 15 to 30 minutes to clear, and into xylol to dissolve the oil and also any paraffin-wax which adhered to the section from the cutting process. From xylol the sections were mounted into Canada balsam.

When using other stains the following procedure was adopted:—

  • Eosin: A 0.5% solution, made by dissolving 0.1 gm. dry eosin in 20 c.c. of 50% alcohol was used as stain. The sections were cleared from chlorophyll in absolute alcohol. Placed in eosin solution as above, diluted with water about 10 times, and left for from half an hour to several hours. Removed into acetic acid (2%) solution for a few minutes. Dehydrated in absolute alcohol. Cleared in clove oil or xylol, or both. Mounted in Canada balsam.

  • Saffranin: Used a solution of 1 gm. of alcoholic saffranin in 50 c.c. absolute alcohol and 50 c.c. water. After clearing, the sections were left in the diluted stain (2 or 3 drops per watch glass of water) for about 15 minutes, then transferred through 50% to 70% alcohol (if necessary, to absolute alcohol) and completed as above.

  • Gentian-Violet: A standard solution of unknown strength was used. Sections, after clearing in methylated spirit or absolute alcohol, were transferred to water and thence placed in the stain for 15 to 30 minutes, washed in distilled water, and then rapidly through absolute alcohol into clove oil. The latter dissolves out the stain rapidly, so that when just at the right strength of staining, the sections were removed into xylol and thence mounted.

Photomicroscopic Procedure.

Photomicrographs were made of normal sections of each species. The apparatus used was assembled and set up by the Chief Inspector and Forest Guard Johnson. A Graphic camera with the lens removed was superimposed over a microscope, the eye piece of which was removed, the end of the tube being connected with the lens aperture of the camera by an overlapping, double roll of black velvet. The camera and microscope were clamped on to a wooden frame, while illumination was obtained by fixing a bulb socket on to the edge of the wood frame and using a 75 watt frosted bulb, daylight being

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excluded by covering the microscope, etc., with a green cloth during the exposure (see Fig. 2). A Wratten K2 filter was fixed just inside the camera lens aperture.

In order to focus more easily than on the ground glass plate, a blank plate was developed, fixed, and utilised as a focussing screen, using a magnifying glass for fine focussing; for roughly focussing the image, a ground glass plate was slipped into the camera at the back of the screen. After experimenting with plates of several types and speeds, it was decided to use Panchromatic B. Imperial plates with an average exposure of one minute. This procedure was followed by Forest Guard Forbes, who carried out most of the photographic work.

No appreciable difference was experienced in the suitability for photography of the different microscopic stains used in the preparation of the sections.

General Discussion of the Characters of Leaves.

Several attempts have been made by different workers to find some one variant factor by which pines can be clasified, but so far it has not been possible to confine identification to one character only, and it has been found necessary in all classifications to employ several factors as determinants; this was found to apply in the present study also.

The structure of a typical pine leaf is shown in Figure 3, but each species has its own characteristic structure varying more or less from the type. Species may vary in “fundamental characters,” i.e., shape of leaf, number and arrangement of ducts and stomata, or character of hypodermal layers, or the fundamental structure in one species may compare exactly with that of a leaf of another species displaying similar characters but differing widely in appearance, owing to minor characteristics. The typical pine leaf is made up of the outer covering skin, the ground or assimilating tissue, and the conducting tissue, but certain botanical features are of particular diagnostic value in this genus, and these are noted below.

In most pine species the needle possesses an inner covering layer of hypodermis, which may consist of one or more rows, immediately inside the epidermis, of specially thick-walled cells whose chief object is the mechanical strengthening of the leaf structure and possibly, in part, the insulation of the inner tissues from exterior influences. In certain species an extra row of thin-walled regular cells, with no cell contents, is interposed between the epidermis and the first thickened hypodermal layer. This is the “water layer,” and so far no specific reason for its existence can be given. Its presence or absence, however, is constant within a species.

Resin canals in the pine needle are formed by the modification of certain cells of the mesophyll parenchyma to act as secretory canals. In section these ducts appear as a ring of a few or many ovate cells with thickened walls surrounding a central passage lined with thin-walled secreting epithelial cells which are continually disintegrating and throwing their contents of resin into the duct. When

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situated immediately adjoining the epidermal or hypodermal layer of cells, the resin ducts are termed “marginal” or “peripheral”; if placed at the inner edge of the mesophyll and adjoining the endodermal layer they are “internal” when the resin ducts appear surrounded by mesophyll cells they are “median.”

In conjunction with the fibro-vascular bundles of the centrally situated fibro-vascular strand of the leaf occur specially adapted conductive tissues—the transfusion tissue and the albuminous cells—while in some species there are found one or more plates of parenchyma cells between the rows of xylem cells. These appear in cross-section of the bundle as a single row of elongated cells, traversing the xylem and phloem radially, and are described as “parenchyma rays.”

The numbers, arrangement, or composition of the structural leaf elements may differ in various species, and thus give a means for the identification of different species. Englemann* attempted to classify pines by the position of the resin ducts, but it would appear that though in general this is constant between species, the leaves within a species vary, and additional resin ducts are often found present and placed in other than the typical position. For example, in P. halepensis (Fig. 9) the resin ducts are typically placed against the hypodermis, but in some needles an extra, medianly placed duct was found. In P. laricio (Fig. 10) the majority of ducts are median, but two or three are present as internal ducts adjoining the endodermis.

The position of the stomata acts as a diagnostic character when taken in conjunction with other features, but again the number of stomata cannot be relied on as constant, since the presence or absence of these organs depends very largely on physiological conditions, e.g., in xerophytic species or in individuals grown under xerophytic conditions the number of stomata per area of leaf surface is reduced compared with the number borne by the same species when grown in a warm, humid situation.

In the present investigation it has been found that, although the numbers of stomatic lines may vary from leaf to leaf within a species, their position, whether borne on all or only on certain faces of the needle, remains constant.

Where stomata are not present on all faces, they are absent on the outer face or morphological lower surface of the leaf as in P. Armandi, P. strobus, P. excelsa, P. monticola.

Discussion of the Classification used in the Key.

From the material examined to date a tentative key was drawn up for the identification of pines from the microscopical characters of their leaf section. This was based on the following diagnostic characters, which are applied in the order given and considered to be “fundamental characters” sufficiently constant within a species to be used for the discrimination of species.

[Footnote] * Englemann, “Genus Pinus” and “Revision of the Genus Pinus.”

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(a)

Shape of cross section of needle.

(b)

Number and position of resin ducts.

(c)

Number and position of stomata.

(d)

Nature of hypodermal tissue.

(a)

The shape of the needle section follows on the number of leaves in the fascicle. Roughly, 5-needle pines have a triangular leaf section, the section of 3-needle pines is a sector of a circle, and leaves of 2-needle fascicles are semi-circular in section.

In the case of certain pines which bear both 2 and 3-needle dwarf shoots, two distinct forms of leaf are found within the species, e.g., in P. caribaea, which produces leaves of semi-circular outline and also those which cut to a sector. In the case of P. caribaea, at least, the fundamental structure does not differ with the different shape of leaf (Figs. 21, 22).

In P. Lambertiana, P. excelsa, P. Torreyana it sometimes occurs that the leaf shows a distinctly 4-sided outline, the additional angle being marked by an enlarged corner epidermal cell, but the extra surface is very narrow, and in no case was found to bear stomata, although these may have been borne on all the other leaf faces.

(b)

As noted above, the number of resin ducts varies, within certain limits, with individual leaves, and though it functions as a broad, indicatory factor in distinguishing between species whose general structure is otherwise similar, it is too variable to act as an indentification character alone; e.g., P. massoniana with 6 to 8 ducts, P. lambertiana, P. strobus ranging from 2 to 3 ducts, P. coulteri with leaves showing 2, 4, or 6 ducts, P. laricio 8 to 10, and P. densiflora specimens with 7 to 10 ducts.

The position of the resin-ducts is found to be constant, but here again minor variations occur in individual trees or leaves within one species. In P. halepensis, P. Armandi, P. yunnanensis, P. patula, P. caribaea, P. laricio, P. tuberculata, and P. resinosa resin ducts occur in more than one position, the normal distribution being evidently augmented by scattered ducts of another origin. This occurs in P. patula (Fig. 26), where the normal ducts are median, but are increased in some instances by additional smaller peripheral ducts. In P. yunnanensis occur two median ducts placed in the normal position at either lateral angle, and the six peripheral ducts scattered on both faces appear to be formed as a breaking apart of a group of hypoderm cells, and are probably rudimentary.

(c)

The number and position of the stomata, as discussed above, are not sufficiently discriminating to act alone as a basis of classification, but though the number varies considerably—even in different leaves of the same species—their position is a constant factor, and serves to distinguish species. In the case of P. flexilis (Fig. 39) and P. strobus (Fig. 43) the species are not distinguishable as regards leaf section, number and position of resin-ducts, or number of hypoderm layers, but they differ in that P. flexilis has stomata on all three faces, while P. strobus possesses approximately the same number of stomatic lines per surface, but these appear only on two

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surfaces. The cross sections of P. strobus and P. excelsa (Figs. 43, 38) are identical as to fundamental characters, and the only distinguishing features are shown in the number of stomata, which in this case appears to be fairly constant, in P. strobus the stomata being always in groups of two or three, while in P. excelsa the stomatic lines run in fives.

(d)

The nature and number of the hypodermal layers are the most variable of the characters used in the key classification. The value of this layer as a distinguishing feature appears in certain cases, notably in the instance of the P. ponderosa group, where the characters of the leaf section of the types recognised as growing in New Zealand, viz., P. ponderosa, P. Jeffreyii, and P. scopulorum, are identical, even the stomatic lines showing no clear distinguishing features, except in the hypodermal layer.

Examination of the leaves of these three types as grown in Rotorua showed, however, that P. scopulorum differed from both ponderosa and Jeffreyii types in having a distinct “water layer” of hypoderm cells. P. Jeffreyii is distinguished further by having not more than two hypoderm layers, one of which is a pseudo water layer, in contrast to P. ponderosa, which possesses three to five rows of sclerenchymatous cells, and to P. scopulorum, which shows two sclerenchymatous layers in addition to the water layer.

Mirov, writing on the distinguishing characters of the various P. ponderosa types growing in North America, shows in P. ponderosa, or “typical western yellow pine,” a consistent presence of the water layer, while in typical P. Jeffreyii the sclerenchyma immediately adjoins the epidermal cells.* In comparing this finding with the characters of the types listed in New Zealand some discrepancy is noticed, and it would appear that, basing comparison on this morphological difference, the type which is known as the “scopulorum” type in New Zealand corresponds with the “typical western yellow pine” of North America, a fact not borne out in macroscopical and growth characteristics.

As a further example of the use of this character it may be noted that P. luchuensis (Fig. 11) and P. thunbergii (Fig. 19) or P. Banksiana (Fig. 6) agree in all the essential characters, but the first species is distinct from both the others in having no water layer.

From the present study a “water layer” is shown to be present in the following species:—

Among 3-needle pines in P. scopulorum, yunnanensis, caribaea, rigida, tuberculata, radiata, leiophylla, patula, taeda; in 5-needle pines in P. Armandi, Lambertiana, strobus, excelsa, Montezumae; in the 2-needle group in Massoniana, pinaster, sylvestris, Banksiana, Thunbergii, muricata, Murrayana, densiflora, resinosa, caribaea.

Work on the examination of the anatomy of pine leaves has been carried out, among others, by Englemann, Matthews, Coulter and Rose, and to a lesser extent by Dallimore and Jackson. On comparing the results of the present study with information published by

[Footnote] *Journal of Forestry. Vol. XXVII, No. 2 (1929).

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  • these workers, certain differences were found to occur in various species. This may be due to consistent difference in structure of New Zealand-grown specimens, or may be due to individual variations which have not been corrected by taking a sufficient number of sections, either on the part of past workers or myself.

A list of the differences which have been noted are given below:

Species. Characters Found in this Study. Characters According to Other Authors.
P. Armandi Resin ducts: 2 marginal, 1 median Resin ducts: 2 median (Dallimore & Jackson).
P. Banksiana Resin ducts: 2 median Resin ducts: marginal (Dallimore & Jackson).
P. canariensis " " 2 marginal Resin ducts: median (Dallimore & Jackson).
P. cembroides var. monophylla " " 2 marginal Resin ducts: 5 median (Dallimore & Jackson).
P. halepensis " " 5 marginal 1 median Resin ducts: marginal (Dallimore & Jackson).
P. Lambertiana " " 3 marginal In primordial leaves resin ducts are peripheral, while in permanent leaves they are median (Matthews).
P. monticola Leaf section: 4 sided Triangular (Matthews).
P. Murrayana Resin ducts: None Resin ducts: median (Dallimore & Jackson).
P. palustris " " 2 internal Resin ducts: median (Dallimore & Jackson, Elwes & Henry).
P. patula " " 2 median 2 internal Resin ducts: median (Dallimore & Jackson, Elwes & Henry).
P. pinaster " " 9 median Resin ducts: 2 median (Matthews).
P. pinea " " None Resin ducts: 2 marginal (Dallimore & Jackson).
P. resinosa " " 2 marginal 1 median Resin ducts: marginal (Dallimore & Jackson).
P. sylvestris Stomata on all faces Stomata on inner face only (Dallimore & Jackson).
P. tuberculata Resin ducts: 3 internal 2 median Resin ducts: median (Dallimore & Jackson).

Explanation of Specific Descriptions.

A detailed description of the leaf section of each species is appended to this report. The species are classified alphabetically in series according to the number of leaves in each dwarf shoot, and to the form of their leaf section.

At the head of each description is given a list of species with similar leaves with which the type might be confused, and a shorter note is added showing the points of difference or distinguishing features in each case. The magnification of all figures is × 62.

In the detailed description each element of the leaf structure is taken in turn from the outer cell layer to the centre. When referring to the stomata the numbers given apply to the average number of stomatic openings situated respectively on the upper face, or upper

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two faces in triangular or sectoral leaves, and on the lower face, which is the plain surface in plano-convex needles. Thus 3 + 3 + 5 indicates the presence of three stomatic lines on the two upper faces and five on the lower face, or 11 + 15, which shows 11 on the plain face and 15 on the are of a plano-convex leaf.

The following list explains technical terms used in the text:

  • Albuminous cells: Parenchymatous cells adjoining and connected to the phloem of the leaf and containing dense cell contents.

  • Collenchyma: Parenchymatous cells with cellulose walls, usually elongated, forming strands under the epidermis and at thickened angles of the leaf.

  • Chlorophyll: Green colouring matter present as granules in certain plant cells and characteristic of the mesophyll tissue.

  • Cuticle: An outer layer of hard thickening produced on the outside epidermal walls.

  • Dwarf shoot: The needle-bearing shoots of pines composed of two or more needles borne in the axils of scale-like leaves which form the leaf sheath.

  • Endodermis: A layer of ground tissue bounding the stele and differentiated as a distinct sheath. The much thickened portion of the lateral walls is termed the “endodermal dot.”

  • Epidermis: The surface layer of leaf cells.

  • Epithelium: A definite layer of cells lining a free surface, especially in botany, an internal surface.

  • Guard cells: The epidermal cells which line the stomatic passage and which control its opening and shutting by alternate contraction and expansion.

  • Hypodermis: A layer of one or more rows of cells situated immediately below the epidermis, and usually with more or less thickened walls.

  • Lumen: The space bounded by the walls of an organ, as the central cavity of a cell.

  • Mesophyll: Thin-walled assimilating parenchymatous tissue forming the ground tissue of the leaf, the cells of which contain green chlorophyll granules, and in pines have their walls infolded or plicate.

  • Palisade cells: The outer row of mesophyll cells with deep plicate infoldings at right angles to the leaf surface, and having the appearance of a palisade layer.

  • Parenchyma: Spongy tissue, the cells of which appear in cross section as of equal dimensions.

  • Parenchyma rays: Plates of parenchyma cells placed vertically and radially between the cell rows of xylem or phloem in the leaf, and appearing in cross section as medullary rays.

  • Phloem: Cells of the vascular tissue specialised for the conduction of assimilated food supply in the plant.

  • Sclerenchyma: Parenchyma tissue in which the walls are specially thickened by the laying down of extra layers of lignin.

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  • Stoma: A pore in the epidermis of the leaf used for the passage of gases between the atmosphere and the inner leaf tissue.

  • Tracheid: An elongated closed cell of the wood tissue provided with secondary thickening on the walls.

  • Transfusion tissue: Strands of tracheidal cells of the conjunctive tissue, consisting, in pines, of tracheids with bordered pits.

  • Vascular bundle: A compact strand of specialised conducting tissue consisting of xylem and phloem separated by a layer of formative tissue or cambium developing both xylem and phloem, together with one or more forms of conjunctive cells.

  • Water layer: A row of thin-walled hypodermal cells immediately adjoining the epidermis, and apparently containing only water.

Key to the Microscopical Identification of Leaves of the Genus Pinus.

  • According to: Character of cross section.

    • Number and position of resin ducts.

    • Number and position of stomata.

    • Nature of hypodermal tissue.

A.

Cross Section—Triangular.

I.—

Resin ducts in twos:

Resin ducts median, stomata on all faces, in pairs P. Montezumae
" " " " fours P. leiophylla
" peripheral " " pairs P. Lambertiana
" " " " fours P. flexilis
" " " two faces only, in pairs P. strobus
" " " two faces only, over four (5 + 5) P. excelsa

II.—

Resin ducts in threes:

Resin ducts median, stomata on all faces P. Torreyana
" " and peripheral, stomata on two faces only P. Armandi

B.

Cross Section—Sector.

I.—

Resin ducts in twos:

Resin ducts median, stomata on all faces, number 15 + 9 + 9 P. taeda
" " " stomata on all faces, number 6 + 3 + 3 P. Sabiniana
" " " stomata on all faces, number 12 + 5 + 5 P. Coulteri (N.I.)
" " " stomata on all faces, number 9 + 5 + 5 P. radiata
" " " internal number 10 + 4 + 4 P. palustris
" " peripheral, stomata on all faces, number 3 + 3 + 3 P. canariensis
" " peripheral, stomata on two faces only, number 3 + 3 P. aristata

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II.—

Resin ducts in threes or fours:

Resin ducts median, with 1 water layer of hypoderm, 4 ducts P. scopulorum
" " " with 1 pseudo-water layer of hypoderm, 2–3 ducts P. rigida " " " with no water layer, but 3–5 rows of sclerenchyma P. ponderosa
" " " with no water layer, but 1 row of sclerenchyma P. Jeffreyii
Resin ducts internal with 1 hypodermal water layer P. caribaea
" " median and internal, with hypodermal water layer P. patula

III.—

Resin ducts five or more:

Resin ducts median, stomata on all faces, number 19-7-7, no water layer P. Coulteri (S.I.)
" " " of internal, stomata on all faces, number 8-5-5, 1 water layer P. tuberculata
" " " and peripheral, stomata on all faces, number 10 + 3 + 3, pseudo water layer P. yunnanensis

C.

Cross Section—Semi-circular.

I.—

Resin ducts absent, stomata 7–11, 1 water layer P. Murrayana
" " " " 6–9, 1 pseudo-water layer P. pinea

II.—

Resin ducts two to four:

Resin ducts median, 2, stomata 11 + 15, 1 water layer P. echinata
" " " 2, stomata 9 + 6, 1 or 2 sclerozed hypodermal layers P. luchuensis
" " " 2, stomata under 9 + 6, 2 hypodermal layers P. Banksiana
" " " "(and internal), stomata under 15 + 11 P. caribaea
" " " "3, stomata 12 + 8, two hypodermal layers P. Thunbergii
" " " "3, stomata 11 + 8, 1 water layer, stomata deeply sunken P. muricata
" " peripheral 2 and median, stomata 7 + 10 P. resinosa

III.—

Resin ducts five and over.

Resin ducts median, 9, stomata 15 + 8 P. pinaster
" " " 8–10, stomata 10 + 9 P. laricio
" " " 14, stomata 14 + 6 P. austriaca
" " peripheral, 6, stomata 6 + 3, two rows of sclerenchyma on are, 1 on base, only 2 resin ducts on upper face P. halepensis
" " " 6–8, stomata 8–8, 1 row of sclerenchyma on all faces P. Massoniana
" " " 7–9, stomata 10–7, no sclerenchyma, but a water layer P. densiflora
" " " 8, stomata 9–9, 1 layer of sclerenchyma, and 1 water layer P. sylvestris

D.

Section 4-sided.

Resin ducts peripheral, 3, stomata 4 + 4 on 2 faces only P. monticola

E.

Section Circular

Resin ducts, 2. peripheral P. monophylla

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Series I—Single-needle Pines (leaf section circular).

P. monophylla (Rotorua). (Fig. 4.)

This species has a characteristic section, and is easily distinguished from monophyllous types of P. sylvestris and P. edulis by its distinct structure.

Leaf Section: Circular, the outline much segmented by stomatic openings.

Epidermis: Circular, irregular, thickened cells.

Stomata: 25–30 evenly distributed around leaf. The guard cells deeply sunken, small, and thickened on inner and part of outer walls; the cells lining the outer passage are also sclerosed, each prolonged into a knob-like projection, and act as outer guard cells; the inner passage bounded by a U-cell.

Hypodermis: 1 row of sclerenchyma.

Mesophyll: 4 or 5 rows of slightly plicate, hexagonal cells, the outer row with palisade infoldings.

Resin ducts: 2 marginal placed opposite the flanks of the vascular bundle; an outer ring of about 15 thickened cells with an inner layer of unthickened lining cells round a large cavity with diameter about one-third of the width of the mesophyll.

Endodermis: Large, regular, circular, unthickened cells.

Vascular strand: Circular, V-B single, in a spreading arc; opposite the protoxylem is a mass of tissue made up of pitted transfusion cells and thick-walled cells with dense contents; opposite the phloem is a group of albuminous cells with cell contents, flanked by pitted transfusion tissue; a few indistinct “rays” traversing xylem and phloem.

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Fig. 4

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Series II—Two-needle Pines (leaf section semi-circular).

P. austriaca (P. nigra var. austriaca). (Rotorua.) (Fig. 5.)

Comparative with: P. laricio, which cannot be distinguished by any fundamental differences; but has fewer resin ducts, sometimes internal, and few stomatic lines. P. austriaca has an uneven, ridged upper surface. P. densiflora, P. sylvestris, which have a similar number of peripheral resin ducts.

Leaf section: Semi-circular.

Epidermis: Regular, oblong, much thickened cells with dot lumen.

Stomata: 8 on upper face, 12 on lower face. Guard cells sunk below level of the hypoderm, thickened on inner face; opening urn-shaped, inner air space bounded by U-cell.

Hypodermis: 1 row of regular cubical cells, with thicker walls than in a water layer, and 1 row of sclerosed cells increased at angles and in groups.

Mesophyll: 3 rows of plicate, 5 lobed cells.

Resin ducts: 14 median, arranged around the stele, small, of about 8 slightly thickened outer cells, lined with epithelial cells.

Endodermis: Small, rounded, slightly thickened cells.

Vascular strand: Kidney shaped; vascular bundles 2, separated by thin-walled parenchyma and a narrow band of thickened cells; immediately bounding the phloem is a band, 1 cell thick, of sclerenchyma cells with contents.

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Fig. 5

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P. Banksiana. (Fig. 6.)

  • Comparative with: P. luchuensis, which differs definitely in no diagnostic characters, and from which P. Banksiana can only be distinguished by its widely separated vascular bundles, and the presence of an indefinite “water layer” of hypodermis.

    • P. caribaea, which has a greater number of stomatic lines.

    • P. Thungergii and P. muricata, with usually 3 resin ducts.

  • Leaf section: Semi-circular and elongated.

  • Epidermis: Regular, cubical, much thickened cells.

  • Stomata: 6 on upper face, 9 on lower face. Guard cells slightly sunk below hypodermis, sclerosed on both walls; opening bounded by crescent-shaped epidermal cells; inner space bounded by U-cell.

  • Hypodermis: A pseudo water layer and one row of sclerosed cells much flattened in places, increased at the angles and in scattered groups.

  • Mesophyll: Two rows increased at corners, of much plicated cells, with distinct palisade infoldings.

  • Resin ducts: 2 median; large, of 1 row of sclerosed cells.

  • Endodermis: Elongated, elliptical cells, thickened on outer and lateral walls.

  • Vascular strand: A flattened ellipse, vascular bundles 2, widely separated by thin-walled parenchyma; on flanks of the phloem are scattered storage cells, and a few pitted transfusion cells are visible; distinct storage “rays” traversing xylem and phloem. N.B.—In many sections examined there were no resin ducts.

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Fig. 6

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P. densiflora. (Fig. 7.)

  • Comparative with: P. resinosa, which has only 2 or 4 resin ducts peripheral, and some median.

    • P. luchuensis, austriaca, muricata, Thunbergii, all of which have median resin ducts.

    • P. Massoniana, which also has one water layer only.

  • Leaf section: Semi-circular.

  • Epidermis: Cubical cells with rounded outer wall and distinct cuticle layer.

  • Stomata: 7–8 on upper face, 10–14 on lower face; often in pairs close together; not sunken; guard cells sunk below hypoderm; inner chamber bounded by U-cell.

  • Hypodermis: 1 row of water layer cells.

  • Mesophyll: 3 rows of plicate, roughly 6 lobed circular cells, with palisade infoldings.

  • Resin ducts: 10–12 peripheral, 3 on the upper plain face; fairly small, of 7–9 thickened cells, with slight epithelial layer.

  • Endodermis: Distinct, elliptical cells thickened on outer wall.

  • Vascular Strand: Elliptical, vascular bundles 2; surrounded by thick-walled parenchyma; on the outer flank of the phloem is a mass of “albuminous” cells with storage cell contents, and outside these a group of transfusion cells.

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Fig. 7

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P. echinata (Rotorua). (Fig. 8.)

  • Comparative with: P. Murrayana, with fewer stomatic lines and vascular bundles widely separated; P. Banksiana, with indefinite water layer, fewer stomata, and bundles very widely separated; P. luchuensis, with no water layer.

  • Section: Semi-circular.

  • Epidermis: Regular, small cells with even outer surface.

  • Stomata: 11 on upper surface, 15 on lower surface, guard cells only slightly sunk.

  • Hypodermis: 1 row of regular, thin-walled water cells and an inner, slightly thickened scleroderm layer.

  • Mesophyll: A distinct palisade layer together with an inner row of plicate parenchyma, increased at angles.

  • Resin ducts: 2 median, of about 12 thickened cells with an inner epithelial layer of cells; sometimes 1–3 median or internal additional small ducts in the lower mesophyll.

  • Endodermis: Elliptical, regular, of large cells thickened on the outer and lateral walls.

  • Vascular strand: Of two vascular bundles, closely placed, with transfusion tissue on the flanks.

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Fig. 8

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P. halepensis (Rotorua). (Fig. 9.)

  • Comparative with: P. Massoniana, which has one hypoderm layer only.

    • P. sylvestris, which has one hypoderm water layer and no sclerosed layer, and with outline much broken by stomata.

    • P. densiflora, which has usually more resin ducts and has a water layer only.

  • Leaf section: Semi-circular.

  • Epidermis: Regular, cubical cells with thickened walls and reduced lumen; much thickened cuticle.

  • Stomata: 3 on upper face, 6 on lower face. Guard cells much sunk below level of hypodermis, thickened on both faces; opening flanked by the projecting tips of epidermal cells, and bounded inside by U-shaped mesophyll cell.

  • Hypodermis: 1 row of thin-walled water layer; with a further sclerosed layer along the lower surface.

  • Mesophyll: Markedly plicate circular cells, with palisade infoldings.

  • Resin ducts: 6 peripheral, sometimes 1 or 2 median; 2 only on upper face; of about 9 thickened cells, around an epithelial layer.

  • Endodermis: Round cells, unthickened.

  • Vascular strand: Elliptical, 2 V-B connected by thickened parenchyma cells; a mass of these also face the protoxylem; a few transfusion cells are scattered on the outer flanks of the bundles; large single thickened parenchyma cells scattered below endodermis. Some “rays” apparent in the phloem.

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Fig. 9

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P. laricio (P. nigra, var. calabrica). (Fig. 10.)

  • Comparative with: P. pinaster, which has a distinct water layer.

    • P. caribaea, which has some resin ducts internal, and up to 15 stomata on the lower face.

    • P. Banksiana, which has 2 resin ducts.

    • P. Thunbergii, which has 2–3 resin ducts.

    • P. muricata, which has a water layer, 3 resin ducts, and deeply sunken stomata.

    • P. Murrayana, which has no resin ducts (in samples examined).

  • Leaf section: Semi-circular.

  • Epidermis: Regular, large, narrowly oblong cells, much thickened.

  • Stomata: 9 on upper surface, 8 on lower surface. The cup-shaped narrow openings bounded by the elongated epidermal cells; guard cells sunk below hypodermis, fully sclerosed.

  • Hypodermis: 1–2 rows of thickened cells, a single row only on the lower surface.

  • Resin ducts: 8–10 median, sometimes 1 or 2 internal; usually of 2 rows of thickened cells, not sclerosed.

  • Endodermis: Very regular, elliptical cells, thickened on lateral walls.

  • Vascular strand: Flatly elliptical, vascular bundles 2, surrounded by large-celled parenchyma. Subtending the phloem is a band of collenchymatous cells. No “rays” visible.

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Fig. 10

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P. luchuensis. (Fig. 11.)

  • Comparative with: P. Banksiana, with widely separated vascular bundles and an indefinite water layer.

    • P. caribaea (2-needle), with many (15–11) lines of stomata.

    • P. Thunbergii and P. muricata, with usually 3 resin ducts and the latter with deeply divided outline.

  • Leaf section: Semi-circular.

  • Epidermis: Regular, much thickened cubic cells, with lumen reduced to a dot; outer cuticle distinct.

  • Stomata: 6 on upper face, 9 on lower face. Deeply sunk, opening bounded by roughly triangular epidermal cells, inner opening bounded by U-cell.

  • Hypodermis: 2 rows of thickened, irregular cells.

  • Mesophyll: 2 rows of plicate cells, showing palisade infoldings.

  • Resin ducts: 2 median, of 1 or 2 rows of slightly thickened cells.

  • Endodermis: Large celled, thickened on lateral walls.

  • Vascular strand: Elliptical, vascular bundles 2, spreading; large cells of sclerenchyma scattered opposite the phloem.

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Fig. 11

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P. Massoniana. (Fig. 12.)

  • Comparative with: P. halepensis and P. densiflora, but differs from the former in having 1 row of sclerosed hypoderm cells on all faces.

  • Leaf section: Semi-circular.

  • Epidermis: Regular, cubical cells; all walls much thickened, giving a dot lumen; outline even.

  • Stomata: 7–8 on upper face, 8–10 on lower face.

  • Hypodermis: 1 or 2 rows of sclerosed hypoderm cells increased at angles.

  • Mesophyll: Much plicated, hexagonal cells with palisade formation on all surfaces.

  • Resin ducts: 6–8 peripheral, on both surfaces, each duct of 1 row of thickened cells surrounding a large cavity approximately 1–16th of the plain face length.

  • Endodermis: Oval cells with thickened outer and adjacent walls, not very distinct from inner parenchyma.

  • Vascular strand: Elliptical; V-B 2, a few transfusion rays through xylem and phloem, scattered thickened parenchyma cells around the bundles.

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Fig. 12

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P. muricata (Rotorua). (Fig. 13.)

  • Comparative with: P. laricio, which has no water layer.

  • P. pinaster, with 9 resin ducts.

    • P. Murrayana, which has no resin ducts and the two vascular bundles widely separated in the stele.

    • P. luchuensis, which has no distinct water layer.

    • P. austriaca, which has 14 resin ducts.

    • P. pinea, with no resin ducts and no water layer.

  • Leaf section: Semi-circular.

  • Epidermis: Deeply broken by stomata; regular, almost cubical cells rounded on outer edge and much thickened.

  • Stomata: 8 on upper face, 11–12 on lower face. Large, sunk below hypodermis; the wide opening bounded by narrow epidermal cells; guard cells completely thickened, inner air space bounded by a U-cell.

  • Hypodermis: 1 “water layer” and one sclerosed layer increased at angles and sometimes in groups.

  • Mesophyll: 2 rows of deeply plicate circular cells, with palisade infoldings on either face.

  • Resin ducts: 2 median; of 10 sclerosed cells.

  • Endodermis: Large oval cells.

  • Vascular strand: Elliptical, vascular bundles 2, surrounded by thin-walled parenchyma; a little transfusion tissue on flanks; distinct “rays” visible.

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Fig. 13

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P. Murrayana (P. contorta var. latifolia). (Fig. 14.)

  • Comparative with: P. laricio, which differs in having many (8–10) resin ducts.

    • P. Banksiana, which has a water layer.

    • P. luchuensis, with V-B not widely apart.

    • P. austriaca, with many (14) resin ducts.

    • P. pinea, of greater size of leaf section.

  • Leaf section: Semi-circular.

  • Epidermis: Regular, almost cubical, thickened cells, rounded on outer edge.

  • Stomata: 7 on upper surface, 11 on lower surface. Guard cells slightly sunk.

  • Hypodermis: 1 row of water layer cells, and 1 row, increased in places, of rounded sclerenchyma.

  • Mesophyll: 2 rows of shortly plicate circular cells.

  • Resin ducts: Nil.

  • Endodermis: Regular, elliptical cells, thickened on outer and lateral walls.

  • Vascular strand: Flattened elliptical, vascular bundles 2, small, surrounded by and widely separated by large, thin-walled parenchyma.

  • N.B.—Dallimore and Jackson, Elwes and Henry, and Mathews give this species as possessing median resin ducts.

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Fig. 14

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P. pinaster (Rot. 2). (Fig. 15.)

  • Comparative with: P. laricio, with no water layer.

    • P. austriaca, with no water layer.

    • P. pinea, with few or no resin ducts, and no parenchyma “rays.”

  • Section: Semi-circular.

  • Epidermis: Regular, cubical, thickened cells with dot lumen.

  • Stomata: 7 on upper face, 15 on lower face. Deeply sunk; guard cells below level of the hypodermis. Tubular opening is bounded by an elongated epidermal cell which is “beaked” at the inner margin, restricting the stomatic opening; inner air space bounded by a U-cell.

  • Hypodermis: 1 “water layer” of large, somewhat irregularly shaped cells, with one or two rows of large, irregularly shaped sclerenchyma cells interrupted at the stomata, increased at angles and with cell walls much thickened.

  • Mesophyll: 2 or 3 rows of deeply plicate, roughly 4–6 lobed, square parenchyma cells.

  • Resin ducts: 9 median, placed around are on the lower face only; of 1 row of 9 sclerosed cells.

  • Endodermis: Large, almost circular cells, scarcely thickened.

  • Vascular strand: Flattened elliptical; vascular bundles 2, large; a row of thickened parenchyma bounds the phloem masses and extends between the bundles. A mass of distinct albuminous cells flanks the phloem masses adjoined by the transfusion tissue. “Rays” distinct in xylem phloem.

Note.—This specimen differs from other types examined, which have (i) only 2 resin ducts; (ii) 20 ducts; the leaves of these types have no water layer.

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Fig. 15

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P. pinea (Rotoura). (Fig. 16.)

  • Comparative with: P. pinaster, which has resin ducts and a distinct water layer, with hypodermal sclerenchyma projecting into the mesophyll between deeply sunk stomata.

    • P. Murrayana, with a distinct water layer and greater number of stomata.

  • Leaf section: Semi-circular.

  • Epidermis: Even, large, much thickened cells; cuticle thin.

  • Stomata: 6 on upper face, 9 on lower face. Guard cells sunk below hypodermis, partly thickened.

  • Hypodermis: 2 rows of thickened cells, the outer layer having the appearance of a water layer, but with thickened walls, the inner row sclerosed.

  • Mesophyll: 3 rows of plicate, 6 lobed cells, with outer deep palisade infoldings.

  • Resin ducts: Nil.

  • Endodermis: Circular cells not distinct from inner parenchyma, slightly thickened on outer walls.

  • Vascular strand: Elongated plano-convex, 2, small vascular bundles, surrounded by small celled parenchyma; xylem very regular, flanked on outer edges by transfusion cells; no rays visible.

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Fig. 16

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P. resinosa. (Fig. 17.)

  • Comparative with: P. luchuensis, which has only median resin ducts, and no water layer.

    • P. halepensis and P. Massoniana, in both of which the resin ducts are bounded by 1 row of cells only.

  • Leaf section: Semi-circular.

  • Epidermis: Cubical, even cells with a dot lumen.

  • Stomata: 7 on upper face, 10 on lower face. Slightly sunk inner chamber bounded by U-cell.

  • Hypodermis: One row of pseudo water layer cells.

  • Mesophyll: 3–4 rows of roughly 6 lobed plicate cells, wth slight palisade infoldings.

  • Resin ducts: 2 median, 4 peripheral, the latter fairly large of 12 thickened cells in a double row; those median are smaller and apparently rudimentary.

  • Endodermis: Of flattened, elliptical cells, thickened on outer walls.

  • Vascular strand: Elliptical, vascular bundles 2, surrounded by thin-walled parenchyma; a little transfusion tissue on flanks; no visible rays.

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Fig. 17

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P. sylvestris (Rotorua). (Fig. 18.)

  • Comparative with: P. halepensis, which has 2 hypoderm layers.

    • P. resinosa, which has fewer resin canals—2–4 peripheral and sometimes 2 median.

  • Leaf section: Semi-circular.

  • Epidermis: Outline broadly crenate, of very regular, narrowly oblong cells with reduced lumen.

  • Stomata: 9–12 on lower face, 8 on upper face. The urn-shaped opening bounded by projecting lips of epidermal cells; guard cells sunk below the hypodermal layer.

  • Hypodermis: A water layer of flattened, thin-walled cells and one row sclerosed cells.

  • Mesophyll: Shortly plicate, hexagonal cells, with granular cell contents.

  • Resin ducts: 8 peripheral, of 1 row of 8–9 irregular spherical, much thickened cells with lumen much reduced.

  • Endodermis: Regular, elliptical, small cells, laterally thickened.

  • Vascular strand: Elliptical flattened; vascular bundles 2, small, separated by a mass of thickened parenchyma cells; a band of collenchymatous cells crosses the stele facing the phloem.

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Fig. 18

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P. Thunbergii. (Fig. 19.)

  • Comparative with: P. Massoniana, with 6–8 peripheral ducts.

    • P. halepensis, with 6–7 ducts, and stomata in lines of 6 + 3.

    • P. muricata, with deeply sunken stomata and hypodermis in groups.

    • P. luchuensis, with 2 layers of scleroderm hypodermis.

    • P. densiflora, with peripheral resin ducts.

  • Leaf section: Semi-circular.

  • Epidermis: Regular, thickened cells with dot lumen.

  • Stomata: 8 on upper surface, 12 on lower surface. Guard cells sunk below hypodermis; crescent-shaped epidermal cells bounding the wide opening.

  • Hypodermis: 1 row of small thin-walled cells next to epidermis, together with 1 row, doubled in places, of larger irregularly shaped sclerosed cells.

  • Mesophyll: Slightly plicate 5–6 lobed cells, with palisade infoldings on both faces.

  • Resin canals: 2 median placed at the angles; of 1 row of sclerosed cells, lined with epithelium.

  • Endodermis: Regular, almost spherical cells.

  • Vascular strand: Elliptical, vascular bundles 2, surrounded by thin-walled parenchyma.

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Fig. 19

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Series III—Three-needle Pines (leaf section, sector).

P. canariensis. (Fig. 20.)

  • Comparative with: P. patula, with internal and median ducts.

    • P. Sabiniana, which has median ducts.

    • P. aristata, which has a characteristic non-plicate mesophyll.

  • Leaf section: Sector.

  • Epidermis: Even, regular, cubical cells with dot lumen.

  • Stomata: 3 + 3 on upper face, 4 to 6 on lower face. Guard cells sunk below hypodermis, outer passage urn-shaped.

  • Hypodermis: 2 or 3 rows of sclerosed cells, increased between stomata to groups of cells projecting into the mesophyll.

  • Mesophyll: 2 rows of plicate, hexagonal cells, the outer row deeply infolded.

  • Resin ducts: 2 marginal; of about 9 sclerosed cells surrounding an epithelial layer.

  • Endodermis: Circular, large, unthickened cells.

  • Vascular strand: Roughly triangular; V-B 2, large, an are of thickened parenchyma subtending the bundles, a few “rays” traversing xylem and phloem.

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Fig. 20

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P. caribaea. (Figs. 21, 22.)

  • Comparative with: P. Banksiana, which has a sclerosed layer and stomata in lines of 6 and 9.

  • Leaf section: Semi-circular or a sector.

  • Epidermis: Regular, square, much thickened, with dot lumen.

  • Stomata: 5 + 5 on each upper face, 12 on lower. Guard cells sunk below hypodermis.

  • Hypodermis: A row of regular thin-walled cells or water layer, in places strengthened by sclerenchyma cells.

  • Mesophyll: 2 rows of deeply plicate 5 lobed cells.

  • Resin ducts: 4 internal; of 1 row of 8 cells thickened, but not sclerosed. Sometimes 2 median ducts.

  • Endodermis: Irregular, almost spherical, cells with outer wall thickened.

  • Vascular strand: Elongated elliptical; vascular bundles 2; with transfusion tissue on the flanks, surrounded by large-celled parenchyma; “rays” visible.

N.B.—In leaves of 3-needle bundles, the two vascular bundles are almost in contact.

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Fig. 21

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Fig. 22

– 546 –

P. Coulteri (Rotorua). (Fig. 23.)

  • Comparative with: P. rigida and P. palustris. This species is distinguished by the greater size of its leaf section and the large proportion of sclerosed hypoderm cells.

  • Leaf section: Sector.

  • Epidermis: Regular, square, thickened cells, with dot lumen.

  • Stomata: 12 + 5 + 5, on all faces; guard cells sunk below epidermal layer, thickened on both walls.

  • Hypodermis: In groups of 3–4 rows thick projecting into the mesophyll between the stomata; of sclerosed cells, increased at angles.

  • Mesophyll: Plicate, 6 lobed cells.

  • Resin ducts: 2 or 4 median, placed at angles and in centre of the lower face; of 1 row of thickened small cells, lined by several broken rows of epithelia.

  • Endodermis: Regular, elliptical cells with thickened outer and lateral walls.

  • Vascular strand: Elliptical, extensive, 2–3 vascular bundles, surrounded by thin-walled parenchyma, and subtended on the upper face by a T-shaped mass of thickened sclerenchyma tissue.

N.B.—In South Island specimens, endodermis has lateral walls only thickened, and V.B. is triple-branched.

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Fig. 23

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P. leiophylla (Rotorua). (Fig. 24.)

  • Comparative with: P. Montezumae, which has a distinct schleroderm layer in the hypodermis.

    • P. excelsa and P. strobus, which have peripheral ducts.

    • P. Armandi, which has stomata on 2 faces only.

    • Leaf section: Triangular.

  • Epidermis: Flattened, ovate cells, with much thickened walls.

  • Stomata: 4 + 4 on upper face, 4 on lower. Guard cells slightly sunken, large, thickened on both faces.

  • Hypodermis: 1 row of unthickened cells, increased at angles and occasionally by several thick-walled cells.

  • Mesophyll: 2 rows of slightly plicate cells, with palisade infolding on all faces.

  • Resin ducts: 2 median; of 2 rows of large unthickened cells surrounding a small cavity.

  • Endodermis: Elliptical cells larger than and distinct from the inside parenchyma, thickened on outer walls.

  • Vascular strand: Circular; 2 V-B surrounded by thin-walled parenchyma, a line of thickened cells joining the bundles; some albuminous cells against the phloem.

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Fig. 24

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P. palustris (Rotorua). (Fig. 25.)

  • Comparative with: P. caribaea, which has occasional median ducts and a distinct water layer, with no sclerenchyma.

  • P. tuberculata, with additional median ducts, and which differs also in having a water layer.

  • Leaf section: A sector.

  • Epidermis: Even, cubical cells with dot lumen.

  • Stomata: 3 + 4 on upper face, 10 on lower. Pores not sunk, guard cells sunk to the level of hypoderm.

  • Hypodermis: 2 rows irregularly increased to 3 rows of sclerosed cells.

  • Mesophyll: 2 rows of slightly plicate 4 lobed cells without a palisade formation.

  • Resin ducts: 2 internal; of an outer row of 12 somewhat thickened cells with an inner row of 9 similar cells, cavity small.

  • Endodermis: Regular, distinct, elliptical cells, thickened on lateral walls.

  • Vascular strand: Elliptical, 2 vascular bundles, spreading; a little transfusion tissue present; “rays” visible in xylem. The tissue opposite the protoxylem appears spongy, and constantly breaks apart, leaving large air spaces.

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Fig. 25

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P. patula. (Fig. 26.)

  • Comparative with: P. canariensis, which has marginal ducts.

  • Leaf section: A sector.

  • Epidermis: Much thickened elliptical cells.

  • Stomata: 3 + 3 on upper face, 6 on lower face.

  • Hypodermis: 1 layer of water cells and an inner, slightly thicker walled, but unsclerosed layer.

  • Mesophyll: 2 rows of plicate, 4 lobed cells, with palisade infoldings.

  • Resin ducts: 2 median and 2 internal, the former of about 10 cells round a large cavity, the internal ducts smaller.

  • Endodermis: Large, almost spherical cells, thickened on the outer and lateral walls.

  • Vascular strand: Slightly elliptical; V-B 2, surrounded by thin-walled parenchyma, with a mass of albuminous cells opposite the phloem, “rays” traversing the phloem.

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Fig. 26

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P. ponderosa (Botanical Gardens, Wellington). (Fig. 27.)

  • This species closely resembles P. Jeffreyi, but in the latter there is no distinct water layer, and only 1 or 2 rows of sclerosed cells.

    • It differs from P. scopulorum in having no water layer in the hypodermis.

    • No definite character distinguishes this section from that of P. rigida.

  • Section: Sector.

  • Epidermis: Regular, cubical cells with dot lumen and distinctly thickened cuticle.

  • Stomata: 3 + 3 on upper face, 8 on lower face. Guard cells deeply sunk to lowest layer of hypodermis; entrance tube bounded by crescent-shaped epidermal cells, and opening at the outer level of the epidermal layer.

  • Hypodermis: 4–5 rows of irregularly shaped sclerenchyma cells.

  • Mesophyll: 3 rows of plicate, hexagonal cells.

  • Resin canals: 3 median placed at the angles; about 25 sclerosed cells in a double row around the epithelial layer.

  • Endodermis: Regular, elliptical, thickened on outer and lateral walls.

  • Vascular strand: Elliptical, large; vascular bundles 2, connected on their lower sides by a narrow band of thickened cells, while a band of sclerosed cells borders the thin-walled parenchyma adjoining the xylem. A mass of “albuminous” tissue flanks the bundles and adjoins the outer transfusion tissue. Several “rays” are visible traversing xylem and phloem.

N.B.—The macroscopical characters of this tree were similar to type P. Jeffreyi.

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Fig. 27

– 551 –

P. Jeffreyi (Rotorua). (Fig. 28.)

  • Comparative with: P. ponderosa and P. scopulorum, the former differs in having 3 to 5 rows of sclerosed hypodermal layer and the latter differs in its distinct water layer.

    • P. Sabiniana, which has no water layer but 2–3 rows of sclerosed hypodermis.

  • Leaf section: Sector.

  • Epidermis: Regular, cubical cells, cuticle thick, outline widely crenated.

  • Stomata: 5 + 6 on upper faces, 8 on lower. Guard cells sunken, thickened on both faces.

  • Hypodermis: 2 rows of thickened but not sclerosed cells, the outer row on the upper faces, with thinner walls.

  • Mesophyll: 2 to 3 rows of plicate, 5 or 6 lobed cells.

  • Resin ducts: 3 median; of about 12 outer thickened cells, with a disintegrating epithelial lining.

  • Endodermis: Elliptical cells, thickened on outer wall.

  • Vascular strand: Flattened, elliptical V-B 2, spreading; a mass of sclerenchyma fronts the lower face of the bundles, which are joined by a line of thickened tissue on the upper face; much transfusion tissue adjoins the vascular tissue.

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Fig. 28

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P. scopulorum (Rotorua). (Fig. 29.)

  • Comparative with: P. ponderosa and P. Jeffreyi, from which it differs in its distinct water layer.

    • P. Sabiniana, which has no water layer.

    • P. rigida, with small resin ducts.

  • Leaf section: A sector.

  • Epidermis: Regular, cubical cells.

  • Stomata: 5 + 5 on upper faces, 8 on lower face. The cells bounding the pore are slightly sunk below the surface, and cause a wide crenation of the leaf outline. Guard cells sunk to level of hypodermis.

  • Hypodermis: 1 distinct water layer and 2 rows of sclerenchyma, increased to 3 or 4 in the groups of the lower face.

  • Mesophyll: 3 rows of plicate cells with palisade infoldings.

  • Resin ducts: 3 or 4 median; of 1 row of 13–15 thickened cells.

  • Endodermis: Large, almost circular cells, thickened on the outer wall.

  • Vascular strand: Elliptical, with 2 vascular bundles surrounded by thin-walled parenchyma, except for an arc of thickened cells subtending the xylem; some transfusion tissue flanks the bundles.

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Fig. 29

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P. radiata (Fig. 30.)

  • Comparative with: P. halepensis, which has 6 peripheral resin ducts and 1 row of sclerosed hypodermis.

  • Leaf section: A sector, occasionally semi-circular, margin crenate, interrupted by stomata.

  • Epidermis: Regular, uniform, square cells with thickened walls and dot lumen.

  • Stomata: 4–6 on each upper face, 7–10 on lower face. Deeply sunken, of characteristic shape, with the outer bordering pair of epidermal cells each prolonged into a sharp beak enclosing an outer stomatal space; the inner guard cells thickened on both outer and inner walls, and the inner air space bounded by a U-cell of mesophyll tissue.

  • Hypodermis: 1 layer of thin-walled pseudo-water layer cells together with 2 rows of regular sclerosed cells.

  • Mesophyll: A palisade layer with 2 or 3 inner rows of plicate cells.

  • Resin ducts: Usually 2 median, but frequently lacking; duct consists of 1 row of 10 cells with unthickened walls and an inner row of secreting cells.

  • Endodermis: Regular large elliptical cells thickened on outer and lateral walls.

  • Vascular strand: Large, elliptical; 2 vascular bundles, surrounded, except on the polar extremities, by thickened parenchyma; between this layer and the endodermis is thin-walled large-celled parenchyma; several “rays” visible in xylem and phloem.

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Fig. 30

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P. rigida. (Fig. 31.)

  • Comparative with: P. ponderosa and P. Jeffreyi, which have no water layer, and with P. scopulorum, which has similar structure but a smaller vascular strand.

  • Leaf section: Sector.

  • Epidermis: Cubical, regular cells.

  • Stomata: 7 + 7 on upper faces, 9 on lower. Openings not sunk, guard cells slightly sunk, thickened on both faces, inner pore bounded by U-cell.

  • Hypodermis: 3 rows of sclerosed cells, the outer row of small, thinner-walled cells, but not a distinct water layer.

  • Mesophyll: 2 rows of 5–7 lobed plicate cells, the outer walls with palisade infoldings.

  • Resin ducts: 2 or 3 median; small, of 9 thickened cells with inner epithelial layer.

  • Endodermis: Regular, distinct, many elliptical cells, thickened on outer and lateral walls.

  • Vascular strand: Elliptical, large, lined with regular thin-walled parenchyma; vascular bundles 2, spreading; xylem regular, with transfusion tissue on flanks, phloem flanked by distinct masses of albuminous cells; no “rays” visible.

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Fig. 31

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P. Sabiniana. (Fig. 32.)

  • Comparative with: P. canariensis, with peripheral resin ducts.

    • P. yunnanensis, with over 5 resin ducts, peripheral.

    • P. patula, with sometimes internal ducts, and a much smaller leaf section.

    • P. palustris, with internal resin ducts.

  • Leaf section: Sector.

  • Epidermis: Outline widely crenate; of regular, square, much thickened cells.

  • Stomata: 4 + 4 on upper faces, 7 on lower face. Guard cells slightly sunk, thickened on inner and part of outer wall.

  • Hypodermis: 2–3 layers of hexagonal, sclerosed cells.

  • Mesophyll: Large, slightly plicate.

  • Resin ducts: 2, median, placed at angles; of 2 or more rows of thickened cells surrounding an epithelial layer.

  • Endodermis: Regular, elliptical cells with laterally thickened walls.

  • Vascular strand: Reniform; 2 V-B connected by thin-walled parenchyma; an are of thickened cells adjoins the phloem.

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Fig. 32

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P. taeda (Rotorua). (Fig. 33.)

  • Comparative with: P. leiophylla and P. Lambertianu, which have no sclerosed hypodermal layer.

    • P. radiata, which is larger, with characteristic stomata and only a pseudo-water layer.

  • Leaf section: A sector.

  • Epidermis: Regular, much thickened cells.

  • Stomata: 4–9 + 4–9 on upper faces, 9–15 on lower face. Slightly sunk; guard cells thickened on both walls.

  • Hypodermis: 1 row of water layer cells and 1 of irregular sclerosed cells, increased at angles.

  • Mesophyll: Slightly plicate, circular cells, slight palisade infoldings.

  • Resin ducts: 2 median; outer layer of 12 slightly thickened cells with epithelial lining.

  • Endodermis: Regular, large celled; with outer and laterally thickened walls.

  • Vascular strand: Cordate; vascular bundles 2, placed close together; parenchyma thin-walled, bundles by transfusion tissue; distinct “rays” present.

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Fig. 33

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P. tuberculata (Rotorua). (Fig. 34.)

  • Comparative with: P. radiata, which differs in having extra resin ducts peripheral and fewer stomata.

    • P. palustris, with no water layer.

    • P. canariensis, without a water layer.

    • P. caribaea, with no scherenchyma layer.

    • P. yunnanensis, which differs in having many (6), marginal ducts, an ill-defined water layer, and only 1 row of sclerosed hypoderm.

  • Leaf section: Sector.

  • Epidermis: Regular, cubical, much thickened cells.

  • Stomata: 5 + 5 on upper face, 8 on lower face. Guard cells sunk, partly thickened on both faces; the bounding epidermal cells large at the base.

  • Hypodermis: A distinct water layer, bounded on the inner side by 1, increased occasionally to 2, rows of sclerenchyma.

  • Mesophyll: 2 rows of deeply plicate, 8 lobed cells; marked palisade infoldings.

  • Resin ducts: 2 median and 2 internal; of an outer row of about 10 unthickened cells and an inner row of 5–6; the ducts are often all median.

  • Endodermis: Large, elliptical, scarcely thickened cells, but thickened on lateral walls with a distinct endodermal dot.

  • Vascular strand: Elliptical; vascular bundles 2, closely placed, and surrounded by much unthickened parenchyma; a mass of transfusion tissue on either flank of the bundles; no “rays” present.

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Fig. 34

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P. yunnanensis. (Fig. 35.)

  • Comparative with: P. tuberculata, with median and internal ducts.

    • P. radiata, which has only median ducts and several hypodermal layers.

    • P. canariensis, with schlerenchyma in groups, stomata in threes.

  • Leaf section: A sector.

  • Epidermis: Regular, oblong cells giving an even, unbroken outline.

  • Stomata: 3 + 3 on upper face, 11 or 12 on lower face. Guard cells slightly sunk, thickened on both faces.

  • Hypodermis: 1 layer of small-sized pseudo water cells and an inner row of larger, slightly thickened cells, slightly increased at angles.

  • Mesophyll: 2 rows of many lobed plicated cells.

  • Resin ducts: 6 peripheral, of which 4 are placed on the lower face and 2 median opposite the angles; composed of 7–9 outer cells, slightly thickened, and an inner layer of thin-walled cells around a small cavity.

  • Endodermis: Regular, elliptical cells, thickened on outer and lateral walls.

  • Vascular strand: Elliptical, V-B 2, spreading; a mass of thickened cells with cell contents lies on the upper part of the stele, subtending the arc of vascular tissue; xylem is divided into groups by the rays which traverse it and the phloem.

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Fig. 35

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Series IV—Five-needle Pines (leaf section a sector, triangular or 4-sided).

P. aristata. (Fig. 36.)

  • Comparative with: P. canariensis, which has stomata on all faces.

    • P. aristata is distinguished by its broad mesophyll of scarcely plicate cells and its characteristic leaf section outline.

  • Leaf section: Irregular sector.

  • Epidermis: Small, much thickened cells, with distinctly circular lumen, and a very thick cuticle layer.

  • Stomata: 3 + 3 on upper faces. Guard cells deeply sunk, thickened on both faces; the sunken opening bounded by the thickened edges of small epidermal cells.

  • Hypodermis: A row of regular, almost circular, collenchyma cells.

  • Mesophyll: A wide band 4–6 cells, large, only very slightly plicate.

  • Resin canals: 2 peripheral; of 16 outer thickened cells lined with disintegrated epithelium; the hypodermal cells are discontinued opposte the duct, which here adjoins the epidermal layer.

  • Endodermis: Elliptical, small, unthickened cells.

  • Vascular strand: Circular, lined by large-celled parenchyma; V-B single; adjoining the phloem is an arc-shaped layer of somewhat thickened cells with contents; much pitted transfusion tissue on upper flanks.

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Fig. 36

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P. Armandi (Rotorua). (Fig. 37.)

  • Comparative with: P. Lambertiana and P. flexilis, which have stomata on all faces.

    • P. strobus, which has 2 resin ducts and stomata in pairs or threes.

    • P. excelsa, which has 2 ducts and stomata in fives.

    • P. Montezumae, which has median ducts.

  • Leaf section: Triangular.

  • Epidermis: Regular on lower surface, irregular and broken on upper faces on account of protruding cells between the closely placed stomata.

  • Stomata: 4–5 + 4–5 on upper faces only. Guard cells thickened on both surfaces, slightly sunk, to the level of the hypoderm layer.

  • Hypodermis: 1 row of water layer cells.

  • Mesophyll: 2 rows of plicate, hexagonal cells on upper surfaces, 1 row, with palisade arrangement, on the lower face.

  • Resin ducts: 2 peripheral on lower face, sometimes an extra median duct placed at the upper angle; ducts of 1 row of 6 thin-walled cells, lined with epithelium.

  • Endodermis: Of large, almost circular cells, with sclerosed dividing wall.

  • Vascular strand: Circular; V-B single, occupying practically all the stele; but surrounded by a thin-walled parenchyma layer of large cells.

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Fig. 37

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P. excelsa. (Fig. 38.)

  • Comparative with: P. strobus, which has fewer stomata.

    • P. flexilis, which has no water layer.

    • P. Montezumae, which has median resin ducts.

    • P. Lambertiana, which has stomata on all faces.

  • Section: Triangular, sometimes 4-sided, with enlarged epidermal cells marking the angles.

  • Epidermis: Very small, thick-walled cubical cells.

  • Stomata: 5 + 5 on upper faces only. Slightly sunk; epidermal bounding cells protruding when open.

  • Hypodermis: 1 row of thin-walled water layer of flattened cells.

  • Mesophyll: Large, plicate cells.

  • Resin ducts: 2 peripheral; of large, almost circular, cells thickened on outer and adjacent walls; 1 row of lining cells.

  • Vascular strand: Circular; vascular bundle single, surrounded by fairly thick-walled parenchyma, with a mass of thin-walled tissue subtending the protoxylem.

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Fig. 38

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P. flexilis (Rotorua). (Fig. 39.)

  • Comparative with: This species differs from P. Montezumae, P. leiophylla, and P. taeda in having peripheral ducts; from P. strobus and P. excelsa in having stomata on all faces; from P. Lambertiana in having no water layer.

  • Leaf section: Triangular.

  • Epidermis: Small, thick-walled cells, radially flattened.

  • Stomata: 3 + 3 + 3 borne on all faces. Guard cells slightly sunk, thickened on both faces.

  • Hypodermis: 1 layer of sclerosed fairly regular cells, increased at angles.

  • Mesophyll: Shortly plicate, 4 lobed cells.

  • Resin ducts: 2 peripheral, on lower face; 1 row of thickened cells and an inner thin-walled layer.

  • Endodermis: Elliptical cells, with thickening on the lateral walls between the cells.

  • Vascular strand: Circular; V-B single, surrounded by thin-walled parenchyma, a few transfusion cells flanking the phloem; 2 or 3 “rays” visible in phloem and xylem.

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Fig. 39

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P. Lambertiana (Rotorua). (Fig. 40.)

  • Comparative with: P. flexilis, which has no water layer.

    • P. strobus and P. excelsa, which have stomata only on upper faces.

    • P. Montezumae, which has median resin ducts.

  • Leaf section: Triangular or 4–5-sided, the angles defined by enlarged epidermal cells.

  • Epidermis: Small flattened, oval cells, with much thickened walls; the cells adjoining the stomatic opening are prolonged into a rounded beak, which probably form the ridges felt on the leaf surface.

  • Stomata: 2–3 + 2–3 + 3 on all faces. Guard cells slightly sunk, walls strengthened on both faces; large posterior air spaces, bounded by several cells.

  • Mesophyll: Large, slightly plicate, circular cells, with slight palisade infoldings on all faces.

  • Hypodermis: One row of pseudo water layer.

  • Resin ducts: 2 on lower face and sometimes 1 in upper angle, peripheral; surrounded by a row of uneven sized cells, a thinner walled continuation of the hypoderm layer, and lined by thin-walled epithelium.

  • Endodermis: Elliptical cells with distinct sclerosis of adjacent walls.

  • Vascular strand: Circular, V-B single, surrounded by large-celled, thin-walled parenchyma, with scattered cells of transfusion tissue (with bordered pits) on flanks of bundle.

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Fig. 40

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P. Montezumae. (Fig. 41.)

  • Comparative with: P. leiophylla, which has no definite sclerenchyma layers.

    • P. excelsa, P. strobus, and P. flexilis, with peripheral ducts.

    • P. Armandi, with peripheral ducts and stomata only on two faces.

  • Leaf section: Triangular or 4-sided.

  • Epidermis: Small, oval, much thickened cells.

  • Stomata: 2 + 2 + 4; not sunk; guard cells thickened on both faces.

  • Hypodermis: An irregular layer of thin-walled water layer cells and 1 inner row of sclerosed, large cells, with contents, increased only at angles.

  • Mesophyll: 2 rows of plicate cells.

  • Resin ducts: 2 median, at the lower angles; of about 10 slightly thickened cells, with internal epithelial layer.

  • Endodermis: Irregular circular cells, thickened on outer walls.

  • Vascular strand: Circular; with 2 small vascular bundles, the phloem subtended by a line of sclerosed cells.

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Fig. 41

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P. monticola. (Fig. 42.)

  • [The section below cannot be correctly rendered as it contains complex formatting. See the image of the page for a more accurate rendering.]

    Comparative with: P. Lambertiana, which slightly resembles P. monticola, but the latter can be easily identified by its 3 large marginal ducts, each with a diameter of about 1/7 of the leaf diameter.

  • Leaf section: 5-sided, sometimes 4-sided.

  • Epidermis: Very small, rounded cells, protruding between stomata and giving an irregular outline.

  • Stomata: 4 + 4 on lateral faces; the short upper faces bear no stomata; nil on lower face. Guard cells sunk, thickened on both faces; the cells bounding the outer passage somewhat sunk and with a protruding tip.

  • Hypodermis: 1 row, occasionally increased to 2 rows, of sclerenchyma cells.

  • Mesophyll: 3 rows of regular, plicate, 6 lobed cells, with slight palisade infoldings on all faces.

  • Resin ducts: 3 peripheral; 1 row of flattened and thickened cells surrounding a large cavity.

  • Endodermis: Elliptical, distinct cells, thickened on outer and lateral walls.

  • Vascular strand: Circular, V-B single; the xylem subtended by an arc of sclerenchyma and flanked by transfusion tissue; a mass of albuminous cells adjoins the phloem, distinct “rays” traversing xylem and phloem.

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Fig. 42

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P. strobus (Rotorua). (Fig. 43.)

  • Comparative with: P. excelsa, which has stomata in fives.

    • P. flexilis, which has no distinct water layer and stomata on lower face.

    • P. Montezumae, which has median resin ducts.

    • P. Lambertiana, which has stomata on all faces.

  • Leaf section: Triangular.

  • Epidermis: Ovate cells, cuticularised, and much thickened, with reduced lumen.

  • Stomata: 3 + 3 on upper faces only. Guard cells slightly sunk to level of hypoderm layer.

  • Hypodermis: 1 layer of slightly thickened cells, not increased at the angles.

  • Mesophyll: Almost circular, infolded to form five lobes; a distinct palisade layer on all faces.

  • Resin ducts: 2 peripheral on lower surface; fairly large, with 1 slightly thickened row of cells, lined by an epithelial layer.

  • Endodermis: Elliptical cells, slightly thickened on outer and adjacent walls.

  • Vascular strand: Circular; V-B single, surrounded by thin-walled, large-celled parenchyma; immediately adjoining the phloem are a few scattered large cells filled with contents, probably reserve storage (albuminous cells); traversing xylem are 2–3 “rays” of cells with contents, continued into the phloem.

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Fig. 43

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P. Torreyana (Rotorua). (Fig. 44.)

  • Differs from all other species with triangular leaf sections by its characteristic, large size.

  • Leaf section: Triangular.

  • Epidermis: Regular, square cells, with thickened walls and reduced lumen.

  • Stomata: 7–8 on each surface. Guard cells sunk below hypodermis, outer wall thickened, opening cup-shaped, flanked by elongated, oblong epidermal cells.

  • Hypodermis: 3–4 rows of sclerosed irregular cells.

  • Mesophyll: Plicate, 6 lobed cells, with distinct palisade infoldings.

  • Resin ducts: 3 median, placed at the angles; each consists of 2 rows of thin-walled cells lined with epithelium.

  • Endodermis: Elliptical cells, thickened on outer and lateral walls.

  • Vascular strand: Circular; V-B 2, connected by thin-walled parenchyma; a bar of thin-walled empty cells joins the bundles opposite the phloem; and an arc-shaped mass of similar parenchyma cells faces both bundles opposite the xylem.

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Fig. 44

Acknowledgments.

The writer is glad to acknowledge here the assistance of Forest Guards Forbes and Johnston in the preparation of the microphotographs, and also the help given by Messrs W. Barker, S. Gibson, and S. Masters, of the State Forest Service, in the scale enlargement of all the plates, while thanks are due to Professor Kirk, Victoria College, for granting permission and facilities, and to Messrs C. E. Palmer, M.Sc., and J. S. Reid, B.Sc., for preparing the microphotographs of Figs. 8, 30, 33

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[The section below cannot be correctly rendered as it contains complex formatting. See the image of the page for a more accurate rendering.]

Index and Summary of Leaf Characters.
Fig Species Cross Section of Needle. No. and Position of Resin Ducts* No of Stomatic Lines Nature of Hypodermis
Upper Surface Lower Surface Water Layer. Sclerosed Rows
Series I—Single-needle Pines (leaf section circular).
4 P. monophylla C 2P 29 1
Series II—Two-needle Pines (leaf section semi-circular).
5 P. austriaca ½C 14M 8 12–14 2–3
6 P. Banksiana ½C 2M 6 9 1 1
7 P. densiflora ½C 7–10P 7 10 1
8 P. echinata ½C 2M 11 15 1 1
9 P. halepensis ½C 1M; 6P 3 6 (2 on arc, 1 on base)
10 P. laricio (nigra val, calabrica) ½C 8–10M; 31 9 10 1 or 2
11 P. luchuensis ½C 2M 6 9 2
12 P. Massoniana ½C 6–8P 6, 8 8–10 1 or 2
13 P. muricata ½C 3M 8 11 1 2 in gps.
14 P Murrayana (conlorta var. latifolia) ½C nil 7 11 1 1
15 P. pinaster—Rotorua - ½C 9M 8 15 1 2 in gps.
P. pinaster — Wellington - ½C 2M 8 15 2 in gps.
16 P. pinea - ½C nil 6 9 2
17 P. resinosa ½C 2–4P; 2M 7 10 1
18 P. sylvestris ½C 8P 9 9 1 1
19 P Thunbergii ½C 2–3M 8 12 1 1
Series III—Three-needle Pines (leaf section a sector or triangular).
20 P. canariensis S 2P 3, 3 3 2–4 in gps.
21 P. caribaea S 4I 5, 5 12 1
22 P. caribaea ½C 2M; 21 11 15 1 occasional
23 P. Coulteri—Rotorua S 2–4M 5, 5 12 3 in gps.
P. Coulteri — South Island S 6M 7, 7 19 1? 2–3 in gps.
24 P. leiophylla 3 or 4 2M 4, 3 4 1–2
25 P. palustris S 2I 3, 4 10 2–3
26 P. patula S 2M; 21 3, 3 6 1 1
27 P. ponderosa S 3M 3, 3 8 3–5
28 P. Jeffreyi S 3M 5, 6 7 1? 1
29 P. scopulorum S 4M 5, 5 10 1 2
30 P. radiata S 2M 5, 5 9 1 2–3
31 P. rigida - S 2–3M 7, 7 9 1? 3 in gps.
32 P. Sabiniana S 2M 3, 3 6 2–3
33 P. taeda - S 2M 9, 9 9–15 1 1
34 P. tuberculata S 2M; 3I 5, 5 8 1 1–2
35 P. yunnanensis S 2M; 6P 3, 3 10 1? 1
Series IV—Five-needle Pines (leaf section triangular, a sector or five-sided).
36 P. aristata S 2P 3 3 1
37 P. Armandi 3 2P; 1M 4, 4 1
38 P. excelsa 3 & 4 2P 5, 5 1
39 P. flexilis 3 2P 3, 4 3 1
40 P. Lambertiana 3 & 4 2–3P 2, 2 2 1?
41 P. Montezumue 3 & 4 2M 2, 3 4 1 1
42 P. monticola 5 3P 4, 4 2
43 P. strobus 3 2–3P 3, 3 1
44 P. Torreyana 3 & 4 3M 8, 7 9 3

[Footnote] * 1 = internal; M = median; P = peripheral.

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Fig. 1.—Swinging microtome fitted with special knife.
Fig 2.—Photomicrographic apparatus.

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Fig. 3.—Transverse section of a typical pine leaf (P. pinaster)