Art. XXX.——Notes from Canterbury College Mountain Biological Station, Cass.
No. 7.—The Rosette Plants: Part I.
[Read before the Otago Institute, 9th December, 1919; received by Editor, 31st December, 1919; issued separately, 30th June, 1920.]
At the end of 1918 the author was able, through the kindness of Dr. Chilton, of Canterbury College, to pass a short time at the Canterbury College Mountain Biological Station, at Cass. During this visit material was collected for an account of all the rosette plants of the district, but the author has been able to study only a few of the plants; hence in the present paper the anatomy only is dealt with. The author hopes, in a subsequent paper, to work out the anatomy of the rest of the rosette plants, and to consider the conclusions drawn from such anatomical study.
The following list gives the names of all the indigenous rosette plants to be found in the vicinity of the station. This list is taken from the list of species compiled by Cockayne and Foweraker.*
Ranunculus multiscapus Hook. f.
—— depressus T. Kirk var.
Cardamine heterophylla (Forst. f.) O. E. Schulz var.
Geum parviflorum Sm.
Geranium sessiliflorum Cav. var. glabrum Kunth.
Viola Cunninghamii Hook. f.
Anisotome filifolia (Hook.f.) Cockayne and Laing.
—— aromatica Hook. f. var.
Angelica montana (Forst.) Cockayne.
Gentiana corymbifera T. Kirk var.
Myosotis australis R. Br. var.
Plantago spathulata Hook. f.
—— triandra Berggr.
Wahlenbergia albomarginata Hook.
Brachycome Sinclairii Hook. f.
Celmisia spectabilis Hook. f.
—— Lyallii Hook. f.
Gnaphalium Traversii Hook. f.
Senecio bellidioides Hook. f. var.
glabratus T. Kirk.
—— Lyallii Hook. f.
—— lautus Forst. f. var. montanus Cheesem.
Microseris scapigera Sch. Bip.
Taraxacum magellanicum Comm.
[Footnote] * L. Cockayne and C. E. Foweraker, Notes from the Canterbury College Mountain Biological Station: No. 4—The Principal Plant Associations in the Immediate Vicinity of the Station, Trans. N.Z. Inst., vol. 48, pp. 166–86, 1916.
1. Geum parviflorum Sm.
This plant is found in rocky situations. The appearance of the plant is shown in figs. 1 and 2, fig. 1 being that of a plant growing in a shaded, damp station, fig. 2 of a plant growing in a more exposed position. The leaves are 1½–6 in. long, either erect or more or less prostrate; they are imparipinnate, the leaflet at the end being a large, crenate leaf, while the
lateral leaflets are small, most of them being quite minute. The leaves are hirsute on both surfaces, and also on the petiole; while on the petiole, especially near the base, there are long, brown, silky hairs. The root-system is well developed, and consists of a mass of tough, wiry, fibrous roots, which bear many branches.
Leaf (figs. 3–10a).—In the leaf all the large veins, especially the midrib, are prominent on the under-surface. The upper epidermis (figs. 4 and 5) consists of fairly large cells, more or less oval in transverse section, which have thickened walls, the outer walls being the more thickened. In surface view these cells are irregular in outline. Stomata are numerous, there being
about 75 per square millimetre on the upper surface. The lower epidermis is similar to the upper, except that the cells are somewhat flatter as seen in transverse section, and as seen in surface view they are more irregular in shape, the cell-walls having a wavy outline. On the lower surface stomata are more numerous, there being about 230 per square millimetre. The stomata are at the same level as the epidermal cells, and the guard-cells have thick walls. On both surfaces of the leaf there are hairs, which are
Fig. 3.—Geum parviflorum. Transverse section of leaf (× 36). a, upper epidermis; b, palisade tissue; c, spongy tissue; d, xylem; e, phloem; f, aqueous tissue; g, long unicellular hair; h, short unicellular hair.
Fig. 4.—Geum parviflorum. Transverse section of leaf (× 175). a, upper epidermis; b, stoma; c, palisade tissue; d, spongy tissue.
Fig. 5.—Geum parviflorum. Upper epidermis of leaf (× 175). a, cells round base of hair; b, base of hair.
Fig. 6.—Geum parviflorum. Lower epidermis of leaf (× 36). a, club-shaped hair; b, long unicellular hair; c, cells above vascular bundles.
Fig. 7.—Geum parviflorum. Club-shaped hair (× 175).
Fig. 8.—Geum parviflorum. Base of long unicellular hair (× 175). a, hair; b, cushion round base.
Fig. 9.—Geum parviflorum. Transverse section of petiole (× 36). a, aqueous tissue; b, bundle-sheath; c, xylem; d, phloem.
Fig. 10a.—Geum parviflorum. Transverse section of base of petiole (× 24). a, tannincontaining cells; b, bundle-sheath; c, xylem: d, phloem; e, sclerenchyma.
of several kinds (figs. 5–8). There are on both surfaces of the leaf long, stiff, bristly, unicellular hairs, which are prolongations of epidermal cells and which have thick walls. Hairs of this type are scattered over the upper surface of the leaf, also on the petiole, and on the lower surface of the leaf they arise from the epidermal cells in the vicinity of the vascular bundles (fig. 6). The epidermal cells round many of these are somewhat larger than the others, forming a kind of cushion round the base of the hair (figs. 5 and 8). In addition to the above-described unicellular hairs, there are much shorter, thinner unicellular hairs, both on the leaf (especially the lower surface) and the petiole (figs. 3, 6, 10). Hairs of a third kind (figs. 6 and 7) are found near the vascular bundles on the lower surface of the leaf: these are club-shaped, multicellular, glandular hairs; they consist of 3 or 4 cells, of which the basal cell is thick-walled and contains only a small amount of protoplasm; the other 2–3 are thin-walled and filled with granular protoplasm. The end cell is much larger than the others.
The chlorenchyma (figs. 3 and 4) is differentiated into palisade and spongy tissue. The former consists of two layers of cells which are fairly compactly arranged; the spongy tissue is nearly twice as wide as the palisade, and is composed of rounded or irregular cells with larger air-spaces between them. In both the cell-walls are slightly thickened, and there are numerous large oval chloroplasts.
In the midrib (fig. 3) there are usually three vascular bundles, of which the central one is the largest. Each vascular bundle is surrounded by a small amount (a layer about 3 cells deep) of colourless parenchyma. Practically the whole of the midrib is filled with an aqueous tissue consisting of large cells with slightly thickened walls; these cells are circular in transverse section and are closely arranged. Just above the vascular bundle some of these cells contain a few chloroplasts. In the midrib, the lower epidermis consists of cells which are small, thick-walled, and, in transverse section, circular. The cuticle here is somewhat thicker. The layer of cells next to this epidermis has thicker walls than the rest of the aqueous tissue, and the cells themselves are smaller. The xylem consists of vessels which are circular in section, of small diameter, and with thick walls; with the vessels there is xylem parenchyma; the phloem is composed of sievetubes, companion cells, and a little parenchyma. Below the phloem there is a small mass of sclerenchyma.
Petiole (fig. 9).—This diagram is of half the petiole. The epidermis consists of very small cells in which all the walls are thickened, especially the internal and external walls; a cuticle somewhat thicker than that in the leaf is present. Stomata are found on both surfaces. Some of the epidermal cells are produced into the two kinds of hairs described in connection with the leaf. The short hairs are much more numerous than the long ones. Practically the whole of the ground-tissue forms an aqueous tissue in which the cells are large, rounded or polygonal, with slightly thickened cellulose walls, and are closely arranged so that there are only minute air-spaces between the cells. The three layers of cells just inside the epidermis are smaller, and have thicker walls; in these cells there are a few chloroplasts.
The vascular bundles are arranged in the form of a crescent, the largest being at the centre. Each vascular bundle is surrounded by a sheath of cells, which is clearly distinguished owing to the fact that the cells contain tannin. Round the sheath the cells of the ground-tissue are much smaller. The vascular bundles are the same as in the leaf, except that wood-vessels
are more numerous, of larger diameter, and more irregular in section. Surrounding the xylem and phloem (between these and the sheath) is small-celled tissue—above the xylem parenchyma, and below the phloem sclerenchyma.
Base of Petiole (fig. 10a).—The epidermis of the upper surface consists of small cells, usually oval in transverse section, with thin lateral walls but thicker internal and external ones. A thin cuticle is present, and there are no stomata. The cells of the lower epidermis are smaller than those of the upper, and have thicker walls. In the upper surface the cells of the layer adjacent to the epidermis are large, oval or irregular in shape, with slightly thickened walls. The rest of the ground-tissue consists of large, more or less circular, closely packed cells, many of which contain tannin. Near the lower epidermis there is a layer of smaller cells with thickened walls, also containing tannin; the lower epidermal cells contain tannin. The vascular bundles, of which there are three, all large, are of the same structure as in the upper part of the petiole. In this part, however, the cells of the bundle-sheath are suberized. The parenchymatous elements of both xylem and phloem contain tannin.
Fig. 10b.—Geum parviflorum. Transverse section of root (× 230). a, dead cortex; b, old cork cells; c, young cork cells; d, cortex; e, phloem; f, xylem; g, starch-containing cells; h, pith.
Root (fig. 10b).—This is a diagram of a section of one of the older roots. On the outside are the remains of the old cortical cells. Then comes a layer of cork-cells, all of which contain tannin, and have thick walls; which are, however, only slightly suberized. Internal to the phellogen is cortex, consisting of irregular cells which have thick cellulose walls, and most of which contain tannin. The pith consists of closely arranged rounded or polygonal cells which have thick walls, and many of which contain tannin. Some of the cells also contain starch, in the form of large rounded grains. The xylem and phloem form a continuous cylinder, the amount of phloem being small. In the xylem the number of vessels is few; these are oval or circular in section, and thick-walled. The rest of the xylem consists of wood-fibres, which are thick-walled and polygonal in shape, almost free from tannin, but containing a large amount of starch.
2. Cardamine heterophylla (Forst. f.) O. E. Schulz var.
This plant is a slender, almost glabrous herb. Practically all the leaves are radical; these are 1–4 in. long, and are imparipinnate, the terminal leaflet being much larger than the others, of which there are usually two
pairs. The leaflets are rounded or irregularly lobed, with entire margin. A few of the leaves, the shorter ones, have only one leaflet. The flowering-stems are 1–5 in. high, and usually bear a few small leaves, which have usually only 1–3 leaflets (fig. 11). The root-system is well developed, consisting of a main tap-root, which gives rise to numerous branches.
Fig. 12.—Cardamine heterophylla Transverse section of portion of leaf (× 175). a, small guard-cell of stoma; b, hair; c, palisade tissue; d, xylem; e, phloem; f, spongy parenchyma; g, large epidermal cell.
Fig. 13.—Cardamine heterophylla. Upper epidermis in surface view (× 175).
Fig. 14.—Cardamine heterophylla. Lower epidermis in surface view (× 175).
Leaf (figs. 12–14).—Both the upper and the lower epidermis consist of cells which vary considerably in size, both in section and in surface view; some of the cells are small, others very large, and slightly convex on the outer surface, so that they project somewhat beyond the level of the other
cells. The cell-walls are thin in both upper and lower surfaces, especially the latter, and here the cells, as seen in surface view, are even more irregular in outline than those of the upper (figs. 13 and 14). Stomata, in which the guard-cells are very small, are found on both surfaces, but are more numerous on the lower; on the upper surface there are about 65 per square millimetre, and on the lower about 105. A few of the cells of the upper epidermis (fig. 12) are produced into long, unicellular, thick-walled hairs, the walls of which are covered with small excrescences of calcium oxalate. On both surfaces is a thin cuticle.
The chlorenchyma is differentiated, although in parts not too clearly. The palisade parenchyma consists of large, thin-walled, more or less oval cells which vary in size and which contain numerous small oval chloroplasts. This layer is usually only one cell deep. The spongy tissue, which occupies the greater part of the leaf, consists of oval or irregular cells which are loosely arranged, so that there are large intercellular air-spaces. This tissue also contains numerous chloroplasts.
The vascular bundles are small, and each is surrounded by a little thin-walled colourless parenchyma. The xylem consists of vessels which in section, are small, circular, and thick-walled; associated with the xylem is a small amount of xylem parenchyma. The phloem is of the usual form.
The leaf is thickened at the midrib, where there is an aqueous tissue, consisting of large, roundish or irregular thin-walled cells, in which there are a very few chloroplasts.
Fig. 15.—Cardamine heterophylla. Transverse section of petiole (× 72). a, furrow of upper surface; b, chlorenchyma; c, aqueous tissue.
Petiole (fig. 15).—The petiole is convex on the lower surface, and on the upper is more or less flattened, with a groove running down each side of the midrib. The epidermis is the same as in the leaf, consisting of small cells, together with much larger, somewhat projecting cells. Stomata are found
on both surfaces. There are three vascular bundles—a small one near each, margin, and a larger one, which, is surrounded by a well-marked endodermis, occupying the centre of the petiole. Some of the cells of this endodermis are slightly suberized. The structure of the vascular bundle is the same as in the leaf.
The mesophyll consists of large, thin-walled, more or less circular cells which are closely packed together. At the margin—that is, in the vicinity of the small vascular bundles—the cells are smaller, and they contain abundant chloroplasts. In the other part of the ground-tissue, especially near the epidermis, there are a few chloroplasts, but most of this tissue is the colourless aqueous tissue.
Fig. 16.—Cardamine heterophylla. Transverse section of flower-bearing stem (× 230). a, chlorenchymatous cortex; b, endodermis; c, pericycle; d, phloem; e, xylem-vessel; f, wood-fibre; g, pith.
Flowering-stem (fig. 16).—The epidermis consists of small oval or rectangular cells in which all the cell-walls, but especially the inner and outer, are thickened; there is a thin cuticle. Stomata are present, the guard-cells being somewhat larger than in the leaf; they are protected by small guard-cell ridges. The whole of the cortex, with the exception of the endodermis, is chlorenchymatous. It consists of oval, thin-walled cells which vary in size and which contain numerous small chloroplasts.
The endodermis is a single layer of cells; opposite the vascular bundles the cell-walls in this layer are suberized, but not in the vicinity of the medullary rays. The pericycle consists of small, thin-walled, parenchymatous cells.
There are five vascular bundles, arranged in a circle. The xylem consists of vessels of fairly large diameter, together with small wood-fibres.
Fig. 17.—Cardamine heterophylla. Transverse section of root (× 175). a, suberized cells; b, cortex with starch; c, phloem; d, xylem-vessel; e, xylem parenchyma.
The phloem group is nearly as wide as the xylem. Between the bundles the medullary rays are lignified, consisting of small, rounded, thick-walled cells; the xylem and these lignified elements together form an undulating band. The pith is not lignified, and consists of large, thin-walled, circular cells.
Root (fig. 17).—Diagram is from a section of the tap-root. On the outside are a couple of layers of small, irregular, thin-walled, dead cells which
have their walls suberized. The cortex consists of cells in which the cell-walls, composed of cellulose, are very much thickened; the tissue is compact, with only small intercellular air-spaces. The cortical cells vary considerably in size: in the outer part of the cortex they are large, and irregular in shape; in the inner part they are much smaller, and more or less oval in section. A large amount of starch is stored up in the cortex.
The endodermis and the pericycle are not clearly defined. The xylem occupies the whole of the centre of the root, and is surrounded by a continuous zone of phloem. The vessels of the xylem are scattered; they are of large diameter and have thick walls. Accompanying the vessels there is a large amount of xylem parenchyma which consists of rectangular or irregular thick-walled cells.
3. Plantago Triandra Berggr.
This plant is illustrated in fig. 18. It is a small plant, with a short, thick rootstock bearing numerous radical leaves. These leaves are ½–2 in. long, with irregularly and remotely serrate margins, and sparingly pilose on the
upper surface with short hairs, the lower surface being glabrous. The root-system is short, and consists of a mass of fibrous roots which do not branch very much.
Leaf (figs. 19–22).—The upper epidermis is sparingly pilose, the hairs being long, jointed ones, consisting of about 6 cells (fig. 21). The basal cell is very large and is more or less circular; its diameter is 2–4 times that of the other epidermal cells. This basal cell is thin-walled at the bottom, but at the outside the wall is much thickened. The rest of the cells of the
hair are large, about twice as long as broad, and the apical cell is wedge-shaped; these cells are thick-walled throughout, but are not cuticularized; they contain protoplasm in the form of primordial utricle and protoplasmic strands, and the nucleus is large and oval. The average length of hair is 0.5 mm. The upper epidermal cells are large, with slightly thickened walls, and somewhat irregular in outline (fig. 20). Stomata are numerous (about 155 per square millimetre); the guard-cells have thickened walls, are protected by fairly prominent guard-cell ridges, and are at the same level as the epidermis.
Fig. 19.—Plantago triandra. Transverse section of leaf (× 230). a, hair; b, basal cell of hair; c, stoma; d, palisade parenchyma; e, spongy parenchyma; f, hydathode.
The lower epidermis is similar to the upper, except that the cells are a little longer, but are smaller in section, and stomata are more numerous (about 200 per square millimetre). A very thin cuticle is present on both surfaces. In addition to the hairs described for the upper surface there are hydathodes—sparingly developed on the upper but more numerous
on the lower surface. They are of the capitate form (Haberlandt*). They consist of two parts—(1) the basal portion or foot; (2) the head, of about 2 cells. The cells of this latter portion have thickened, non-cuticularized walls (fig. 19).
The chlorenchyma is differentiated. The palisade tissue consists of 1–3 rows of cells-large, broad cells, the outer layer being composed of cells about twice as deep as broad, the inner layer or layers of cells about as broad as deep. The cells are thin-walled, fairly closely arranged, and contain numerous small ellipsoidal chloroplasts. The spongy tissue also consists of large, thin-walled, oval or somewhat irregular cells, containing a smaller number of chloroplasts. The chloroplasts in the palisade tissue are slightly larger than in the spongy tissue. Beneath each stoma there is a fair-sized air-space.
The vascular bundles are not numerous and are very small. In the midrib there is, between the vascular bundle and the lower surface, a small amount of aqueous tissue, consisting of rounded cells which are
Fig. 20.—Plantago triandra. Upper epidermis of leaf (× 230). a, guard-cells; b, base of hair.
Fig. 21.—Plantago triandra. Jointed hair (× 48).
either colourless or contain a few chloroplasts. The mesophyll above the vascular bundle is not differentiated, and consists of very large cells which contain chloroplasts. Below the midrib the cells of the lower epidermis are much smaller, are circular in transverse section, and have all their walls thickened. Above the lower epidermis, in the midrib, is a single layer of colourless collenchyma.
The vascular bundle of the midrib is small, and is surrounded by a bundle-sheath of fairly large, thin-walled cells, in a few of which there is a small number of chloroplasts. The xylem consists of vessels of small diameter, together with xylem parenchyma. There is also parenchyma with the phloem. Above the xylem and below the phloem there is a small amount of sclerenchyma, consisting of small irregular cells with thick walls.
[Footnote] * Haberlandt, Physiological Plant Anatomy (English translation), p. 491; London, 1914.
Leaf-base (fig. 22).—The leaf-base is elongated and sheathing, colourless, and thickened considerably near the centre, but thin and membranous
Fig. 22.—Plantago triandra. Transverse section of petiole (× 48). a, aqueous tissue; b, xylem; c, phloem; d, bundle-sheath.
at the margins. The upper epidermis consists of large, thin-walled, colourless cells, without any stomata. The outer walls are slightly thicker than the others. The lower epidermis is composed of smaller cells than the upper, and the walls are somewhat thicker.
The ground-tissue consists of large, rounded, thin-walled cells in which the protoplasm is reduced to a very thin layer lining the walls; this tissue is for water-storage. The vascular bundles are small, and of the same structure as in the leaf.
Fig. 23.—Plantago triandra. Transverse section of root (× 175). a, suberized cells; b, cortex; c, endodermis; d, pericycle; e, phloem; f, xylem.
Root (fig. 23).—The vascular cylinder is small, consisting of a central mass of xylem, composed of elements of small diameter, and with thickened, pitted walls; surrounding the xylem is a narrow band of phloem. The pericycle is a single layer of thin-walled cells. The endodermis is well marked, and consists of cells somewhat larger than the cells of the pericycle and with thicker, slightly suberized walls.
The cortex consists of fairly large, thin-walled cells; in an old root, as illustrated, the hairs of the piliferous layer have disappeared, and the subdermal layer of cortical cells have their walls slightly suberized.
4. Brachycome Sinclairii Hook. f.
The appearance of a single rosette is given in fig. 24. The plant is more or less succulent, 1–3 in. high, and practically glabrous. The plant has a short, thick, branching rhizome, and it is by this means that the plant is
able to form mats. The leaves are ¼–2 in. long, broad and rounded at the tip, and gradually narrowed into the flat petiole; they are deeply toothed, and in some cases appear even pinnatifid.
Leaf (figs. 25–27).—In transverse section the cells of the upper epidermis are seen to be large and somewhat squarish, with all their walls thickened, the outer ones considerably, the thickening being equal to about half the depth of the cell-cavity. The stomata, which are numerous, are raised above the cavity of the epidermal cells, but are at the same level as the thickened external walls. The guard-cells have thickened walls and guard-cell ridges. In surface view (fig. 26) the cells of the upper epidermis are seen to be large and irregular or polygonal. A thin, unevenly but not deeply ridged cuticle is present. On the upper surface there are about 220 stomata per square millimetre.
The cells of the lower epidermis (fig. 27) are similar to those of the upper, except that the cell-walls are not so much thickened; in surface view these cells are more irregular in outline than the cells of the upper epidermis. Stomata are not as abundant as on the upper surface; there are 150 per square millimetre. The guard-cells of the stomata of the lower surface are a little smaller than in the upper surface.
The chlorenchyma is differentiated; the palisade tissue occupies about one-third and the spongy parenchyma two-thirds of the mesophyll. In both the cell-walls are very thin. The palisadic cells are oval or oblong in transverse section, about twice as deep as wide, fairly compactly arranged, and containing numerous small rounded chloroplasts. The spongy tissue consists of large, more or less rounded cells, with small air-spaces between the cells; they contain a much smaller number of chloroplasts than the palisade-cells, and form an aqueous tissue.
The vascular bundles are small, and are surrounded by a sheath of thin-walled, colourless cells. The xylem consists of vessels round in section, with thick walls, and of xylem parenchyma. The amount of phloem is small. The leaf is much thicker in the midrib, where the vascular bundle is accompanied by a mass of large, rounded, thin-walled, colourless cells. There is a smaller amount of this colourless tissue with the other bundles.
Petiole (fig. 28).—The petiole is thick and fleshy, being used for water-storage. The upper epidermis consists of large cells in which the lateral walls are thin, and the inner and outer thickened, but not so much as in the leaf-lamina. A cuticle as in the leaf is present. Many of the epidermal
Fig. 25.—Brachycome Sinclairii. Transverse section of leaf (× 230). a, ridged cuticle; b, thick epidermal wall; c, palisade tissue; d, spongy tissue; e, guard-cell ridge.
Fig. 26.—Brachycome Sinclairii. Upper epidermis of leaf (× 230).
Fig. 27.—Brachycome Sinclairii. Lower epidermis of leaf (× 230).
cells contain chloroplasts, and near the centre of the petiole, above the midrib, a few of them are produced into long, unicellular hairs which contain protoplasm. At the margin of the petiole are found a few capitate glandular hairs. The lower epidermis is similar to the upper, except that it does not produce any hairs, and the cells are smaller and contain more chloroplasts. There are stomata on the upper but not on the lower surface.
There are five vascular bundles—a large one at the centre, and four very small ones. The bundle-sheath is not clearly marked off from the small-celled parenchyma surrounding the bundle The structure of the bundles is the same as in the leaf.
The ground-tissue consists of large, rounded, thin-walled, closely arranged cells. The 1–2 layers of these cells adjacent to the epidermis are chloren-chymatous, as also in the tissue in the margin of the petiole. The main bulk of the ground-tissue is, however, colourless, forming an aqueous tissue.
Rhizome (fig. 29).—The epidermis consists of cells which are oval or rounded in transverse section, and which have all their walls slightly thickened, the external being the most thickened. A very thin, uneven, ridged cuticle is present. The cortex consists of large, rounded, colourless cells which have their walls slightly thickened and which form a water-storage tissue. In the inner part of the cortex there are, at intervals, a few secretion-canals which are lined with a layer of thin-walled epithelial cells.
Fig. 28.—Brachycome Sinclairii. Transverse section of petiole (× 72). a, unicellular hair; b, chlorenchyma; c, aqueous tissue; d, xylem; e, phloem.
The endodermis is well marked, consisting of a layer of irregular cells with thin suberized walls. There is no continuous pericycle, but this layer is represented by a number of groups of pericycle fibres, in which the cells have thick, lignified walls and small lumen. The phloem forms a fairly wide band and is continuous round the xylem; it consists of sieve-tubes, companion cells, and a fairly large amount of phloem parenchyma. The xylem joins a practically continuous band of vessels and of wood-fibres with fairly thick walls. It is interrupted by a few uniseriate medullary rays, also with thickened, lignified walls. The pith is solid, and consists of thin-walled, large, round cells.
In an older part of the rhizome the epidermis has disappeared, and the outer layer of the cortex is suberized.
Root (fig. 30).—The central cylinder is small, and is surrounded by a clearly marked endodermis, which, as in the rhizome, consists of irregular, thin-walled, suberized cells. The pericycle consists of a single layer of cells about the same size as the endodermal cells, and with thin cellulose
Fig. 29.—Brachycome Sinclairii. Transverse section of rhizome (× 175). a, cortex; b, canal; c, epithelial layer; d, endodermis; e, pericycle fibres; f, phloem; g, xylem; h, medullary ray.
Fig. 30.—Brachycome Sinclairii. Transverse section of root (× 175). a, suberized cells; b, cortex; c, endodermis; d, pericycle; e, phloem; f, xylem.
walls. The xylem forms a compact triangular-shaped mass, and its elements have thick walls. The phloem forms three large masses, and consists of sieve-tubes, companion cells, and phloem parenchyma, all of which have their elements of small diameter.
The cortex is a wide band of tissue, consisting of large, more or less circular cells, compactly arranged, and with slightly thickened walls.
5. Gnaphalium Traversii Hook. f.
The plant is a small perennial herb ½–1½ in. high. The plant produces a large number of runners (figs. 31 and 32), which give rise to new plants at a short distance from the parent plant, so that fairly compact mats are formed by the runners going in all directions. The leaves are ¼–1½ in. long,
Fig. 31.—Gnaphalium Traversii. Plant (half natural size) to show root-system.
Fig. 32.—Gnaphalium Traversii. Plant (half natural size) to show runners.
spathulate in shape, and clothed on both surfaces, also on the petiole and runner, with a silvery tomentum. The root-system is a mass of tough, fibrous roots.
Leaf (fig. 33).—From the transverse section it is seen that the leaf is very much thickened at the midrib, where there is a large amount of aqueous tissue. The upper epidermis consists of large cells, in which the lateral and inner walls are thin, but the outer are thickened. There is a thin cuticle on both surfaces. The cells of the lower epidermis are much smaller than those of the upper. On both surfaces many of the epidermal cells are produced into long, two-celled hairs, the outer cell being much longer than the basal cell. Stomata are confined to the lower surface, where they are raised above the epidermal cells. The guard-cells are small and have thick walls. Owing to the dense mass of tomentum it is impossible to find the number of stomata per square millimetre.
The mesophyll consists of palisade and spongy tissue. The palisade tissue consists of a single layer of oval cells in which are numerous elongated chloroplasts. The spongy parenchyma, which is compactly arranged, is composed of rounded or oval cells, also containing chloroplasts. All the mesophyll cells are thin-walled.
The aqueous tissue in the midrib consists of large, thin-walled, rounded cells, with small air-spaces between them. Above the lower epidermis in the midrib a single layer of these cells contain chloroplasts.
In addition to the hairs described above, there are club-shaped, glandular hairs, which consist of about 5 cells.
Petiole.—The petiole is very much thickened at the midrib, but is thin at the margin. The upper epidermis consists of fairly large cells, in which the lateral walls are thin, the inner and outer some what thickened. Many of these cells are produced into hairs as in the leaf. Stomata are confined to the lower surface.
The mesophyll consists for the most part of large, thin-walled, rounded or polygonal, closely arranged cells. This tissue is for water-storage. Near the flattened margins of the petiole the cells are smaller and contain a few flattened chloroplasts.
Fig. 33.—Gnaphalium Traversii. Transverse section of leaf, passing through midrib (× 175). a, palisade tissue; b, spongy tissue; c, two-celled hair; d, stoma; e, glandular hair; f, xylem; g, phloem; h, aqueous tissue.
There are three vascular bundles, the one in the midrib being large, the others smaller. Each is surrounded by a small amount of thin-walled, colourless parenchyma; the bundle has the same structure as in the leaf.
Runner (fig. 34).—This is cylindrical in transverse section. The epidermis consists of small cells, much smaller than in the petiole, which have all their walls slightly thickened. Some of these cells are produced into hairs like those in the leaf, except that, while in the leaf they are usually two-celled, in this case they are three-celled.
There are a few stomata, the guard-cells of which are level with the other epidermal cells and have thickened walls.
The cortex consists of large, thin-walled, rounded or somewhat irregular cells which have small air-spaces between them and which form a water-storage tissue. In the outermost layers there are a few chloroplasts, which are smaller than those in the leaf.
Fig. 34—Gnaphalium Traversii. Transverse section of runner (× 230). a, cells with chloroplasts; b, colourless cortex; c, endodermis; d, perioycle; e, phloem; f, xylem; g, pith.
The central cylinder is fairly small, occupying less than half the diameter of the stem. It is surrounded by a well-marked endodermis in which all the cells are large and have suberized walls.
The pericycle is a single layer of small thin-walled parenchymatous cells. The phloem and xylem form a continuous cylinder round the pith, which consists of large, rounded cells with somewhat thickened walls. In the xylem the vessels and fibres are polygonal in section and are thick-walled.
Root (fig. 35).—The diagram is of an old root, in which the piliferous layer has been worn off, exposing the cortex; the outermost layer is of
Fig. 35.—Ghaphalium Traversii. Transverse section of root (× 230). a, suberized cortex; b, cortex; c, endodermis; d, phloem; e, xylem.
small cells with the walls, which are thin, slightly suberized. The rest of the cortex consists of oval or irregular cells with thicker walls, and small air-spaces between the cells.
The endodermis is a single layer of small oval cells with thin suberized walls. The xylem forms a compact central mass, in which the elements are polygonal in transverse section and have thickened walls. The phloem forms a narrow band surrounding the xylem.