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Volume 52, 1920
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Art. XXXI.—Notes on the Autecology of certain Plants of the Peridotite Belt, Nelson: Part I—Structure of some of the Plants (No. 3).*

[Read before the Otago Institute, 10th December, 1919; received by Editor, 31st December, 1919; issued separately, 30th June, 1920.]

25. Cyathodes acerosa R. Br.

Habit.—This plant is an erect, branching shrub, 1–2 ft. high; the branches are woody and spreading, and the bark is black. The leaves are spreading, ¼–⅓ in. long, acerose, linear, rigid, pungent-pointed, glaucous beneath, with 3 to 7 parallel veins.

Anatomy.

Leaf.—The upper epidermis is composed of very regular rectangular cells which have the longer sides at right angles to the surface of the leaf. These cells have very thick mucilaginous cell-walls, and their cavities are very small and contain tannin. There is a thick cuticle.

The lower epidermis consists of small cells which have thick walls (but not nearly as thick as in the upper epidermis). There is a thick cuticle on this surface also. Most of the cells of the lower epidermis are produced into short papillae with very thick, cutinized walls. Stomata are confined to the lower epidermis; the guard-cells are small, and are at the same level as the other epidermal cells.

The chlorenchyma is differentiated into palisade and spongy tissue. The palisade tissue consists of 3 or 4 rows of narrow, elongated cells. The outermost layer has all the cells full of tannin; the others contain small chloroplasts. The outer layer is very compact, but there are small inter-cellular air-spaces in the inner layers.

The spongy tissue occupies about a quarter of the width of the leaf. It is composed of small, irregular, thin-walled cells, many of which contain tannin. There are small intercellular air-spaces in this tissue.

The number of vascular bundles varies from 3 to 7. The xylem and the phloem are both small in amount, and in the parenchymatous elements there is tannin. Below the phloem there is a mass of stereome, consisting of small cells with their walls so much thickened that their cavities are almost obliterated. Above the upper part of the bundle there is a sheath of small cells with unlignified walls.

Stem.—The cork forms a narrow band; it is composed of very small, thick-walled cells which are very closely arranged.

The cortex consists of oval, thin-walled cells, which contain tannin, and which form a compact tissue with very small intercellular air-spaces.

The phloem is composed of small elements; the medullary rays passing through it contain tannin.

The xylem is composed of a moderate number of vessels which have thick walls. The rest of the xylem consists of wood-fibres which have very thick cell-walls and small lumen.

[Footnote] * For Nos. 1 and 2 see Trans. N.Z. Inst., vol. 50, pp. 230–43, 1918, and vol. 51, pp. 136–56, 1919.

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The medullary rays are uniseriate, frequent, and have thickened, lignified walls, and contain tannin.

The pith is solid, and is composed of large polygonal cells with thick, lignified, and pitted walls. The cells contain tannin.

26. Gentiana corymbifera T. Kirk.

Habit.—The plant is a perennial herb. The root is stout, long, and tapering. The stems are simple and rarely branched from the base, stout, erect, terete, 6–20 in. high. The leaves are both radical and cauline. The radical leaves are numerous, rosulate, 1–2½ in. long, ¼–½ in. broad, narrowed into a short petiole. The blade is coriaceous, and rather thick and fleshy. The cauline leaves are few in number, ¾–1½ in. long, linear-lanceolate, and sessile.

Anatomy.

Leaf.—The upper epidermis is composed of large cells which in transverse section are oval. They have all their walls, and especially the external ones, thickened. These cells contain drops of oil. There is a thin, rough cuticle.

The lower epidermis is the same as the upper, except that the cells are somewhat smaller. There is a thin cuticle on this surface also. Stomata are found on both surfaces, but are much more numerous on the lower. The guard-cells are small, and have very thick walls. The stoma is protected by guard-cell ridges which are rather large.

The chlorenchyma is differentiated into palisade and spongy tissue. The palisade tissue consists of 5 rows of large cells with slightly thickened walls. These cells contain very numerous small chloroplasts, and there are small air-spaces between the cells.

The spongy tissue is composed of large, irregular cells, the walls of which are only slightly thickened. There are quite large intercellular air-spaces in this tissue. These cells contain a thin layer of protoplasm in which are embedded small chloroplasts, which are not nearly as numerous as in the palisade tissue; these cells serve as water-storage cells.

The vascular bundles are small and numerous; associated with both the phloem and the xylem there is parenchyma. The bundle is surrounded by a sheath of thin-walled parenchymatous cells which contain a few chloroplasts. Below the main bundle there is a small amount of collenchyma.

Stem.—The epidermis is composed of cells which are large and rounded in transverse section. They have all their walls very much thickened, and there is also a moderately thick, rough cuticle. Some of the epidermal cells contain drops of oil.

Below the epidermis there is a well-marked hypoderma. This consists of cells which are the same as the epidermal cells, and they also have their external walls cuticularized. The hypoderma is in places separated from the epidermis by a large air-space.

The cortex is a wide band; it is composed of large, more or less oval cells which have their walls somewhat thickened. There are very small intercellular air-spaces in this tissue. In the outer part of the cortex the cells contain a few small chloroplasts. All the cortical cells form an aqueous tissue. The endodermis is well marked; it is a layer of large cells with thin suberized walls.

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The phloem is a fairly wide band of tissue; the sieve-tubes are of small diameter, and there is a large amount of phloem parenchyma. There are also small groups of sieve-tubes on the inside of the xylem.

The xylem is a wide band; it is formed for the greater part of very regular rows of wood-fibres with slightly thickened walls. There are no medullary rays. On the inside of the band of fibres there are a few small vessels.

The pith is composed of large thin-walled cells which have small inter-cellular air-spaces between them.

27. Myosotis Monroi Cheesem.

Habit.—This plant is a small perennial herb which is more or less hispid with short, stiff, white hairs. The radial leaves are numerous, ¾–2 in. long, narrow obovate-spathulate, narrowed into a rather long slender petiole, hispid with short, stiff, white hairs on the upper surface, more sparingly so beneath, and sometimes glabrous except the midrib. The cauline leaves are smaller and narrower.

Anatomy.

Leaf (fig. 1).—The upper epidermis consists of large roundish or squarish cells with thin walls, except the external, which are slightly thickened.

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Fig. 1.—Myosotis Monroi. Transverse section of leaf (× 175). a, unicellular hair; b, stoma; c, palisade parenchyma; d, spongy parenchyma; e, xylem; f, phloem.

A very thin cuticle is present. Numerous epidermal cells are produced into long, stiff hairs with small protuberances on their outside walls. Stomata are found on both surfaces of the leaf; the guard-cells are small

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and have thickened walls, and are level with the surface of the leaf; there are guard-cell ridges.

The lower epidermis is the same as the upper, except that the cells are somewhat smaller. There is a thin cuticle on this surface also. The hairs are not nearly as numerous as on the upper surface.

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Fig. 2.—Myosotis Monroi. Transverse section of stem (× 175). a, unicellular hair; b, chlorenchyma; c, aqueous tissue; d, phloem; e, xylem; f, pith.

The chlorenchyma is differentiated into palisade and spongy tissue. The palisade tissue consists of 4 rows of cells—the 3 outer layers are of oval cells, while the 4th consists of cells which are more or less rounded in transverse section. These cells contain numerous large chloroplasts, and there are air-spaces between the cells.

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The spongy tissue consists of very large, irregular, thin-walled cells which are loosely arranged, so that there are large air-spaces. These cells also contain numerous chloroplasts, which are, however, smaller than in the palisade tissue. Just above the lower epidermis there is a single layer of more closely arranged roundish cells with abundant large chloroplasts like those in the palisade tissue.

Surrounding the vascular bundle there is a sheath of small, irregular, thin-walled, colourless, parenchymatous cells. Between the sheath around the midrib and the lower epidermis the cells are smaller, compactly arranged, and contain fewer chloroplasts. The vascular bundle contains only a small amount of lignified tissue.

Stem (fig. 2).—The epidermal cells are small and roundish, and have their external walls somewhat thickened. There is a very thin cuticle. Some of the epidermal cells are produced into hairs like those on the leaf. The stomata are level with the surface; the guard-cells have thickened walls.

Below the epidermis there is a layer of small round cells which have thin walls and which contain numerous chloroplasts. Between this layer of cells and the rest of the cortex there is in most parts a large air-space. Below the air-space the cortical cells vary considerably in size. The first layer consists of roundish cells with fairly numerous chloroplasts; then the cells become much larger. They are more or less polygonal and fairly compactly arranged, so that there are only small intercellular air-spaces. These cells contain a few small chloroplasts; these are found near the corners where three cells meet. Just above the phloem the cells are smaller. All the cortical cells have thin walls.

The amount of phloem is small; the sieve-tubes and the phloem-parenchyma cells are of small diameter.

The xylem forms a continuous band; it consists chiefly of wood-fibres with somewhat thickened walls, and also of a few vessels of small diameter.

The pith is wide and is solid; just below the xylem the cells are smaller, but as we pass inwards the cells get very large; they have thin walls, and are arranged so that there are small intercellular air-spaces.

28. Euphrasia Monroi Hook. f.

Habit.—The plant is a small perennial herb with stems erect or decumbent below, 3–8 in. high, leafy above and sparingly branched. The leaves are rather close-set, spreading, ⅕—⅓ in. long, obovate or obovate-spathulate, obtuse, narrowed to the base but not evidently petiolate, coriaceous, glabrous, and having one short obtuse tooth on each side.

Anatomy.

Leaf (figs. 3—6).—On examining the leaf one observes on both surfaces some well-marked grooves. These are shown in figs. 3 and 4. These grooves are dark brown in colour, and are much more numerous on the lower than on the upper surface. On the upper surface there are only two; these pass from the midrib to the single tooth on each margin of the leaf. On the under surface there is a groove running almost round the leaf close to the margin. This groove is somewhat irregular in outline; from it numerous other grooves branch off. Cheeseman (Manual of the N.Z. Flora, 1906, p. 554) in describing this plant does not mention these grooves. When transverse sections are taken of the leaf it is seen that the grooves are lined with cells which are water-absorbing cells.

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Figs. 5 and 6 show schematically a section through the upper part and the middle of the lamina respectively. From these diagrams it will be seen that small vascular bundles go to the ventral grooves and end just under the cells lining them. It is reasonable to suppose that these cells are for the purpose of absorbing water and not exuding it.

Fig. 7 gives the structure of the leaf in more detail.

Both the upper and the lower epidermis consist of large, regular cells, those of the upper surface being larger than those of the lower. These cells have their external walls slightly thickened, and there is a thin cuticle. Stomata are found on both surfaces; the guard-cells are small, have thickened walls, and are level with the surface. There are small guard-cell ridges.

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Fig. 3.—Euphrasia Monroi. Upper surface of leaf (× 4). a, groove.
Fig. 4.—Euphrasia Monroi. Lower surface of leaf (× 4). a, groove.
Figs. 5, 6.—Euphrasia Monroi. Transverse sections through leaf (× 30). a, vascular bundles; b, cells in grooves.

The chlorenchyma is differentiated, but only to a small extent. Practically the whole width of the leaf is occupied by spongy tissue; the cells just above the lower epidermis are more like spongy tissue, but the transition between the two types of tissue is not very marked. The 3 layers of cells just below the upper epidermis consist of smaller cells which are more or less rounded and have their walls slightly thicker than do the rest of the mesophyll cells. The next 5 or 6 layers of cells are very large, long cells. Just above the lower epidermis the cells are more irregular. All the mesophyll cells contain numerous oval chloroplasts.

In the furrows there are numerous projections for water-absorption. These are formed of 2 cells which have their walls slightly thickened.

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Fig. 7.—Euphrasia Monroi. Transverse section of leaf (× 175). a, stoma; b, upper epidermis; c, mesophyll; d, vascular bundle; e, cell of groove.
Fig. 8.—Euphrasia Monroi. Transverse section of upper epidermis just above the midrib. a, excretory hair.
Fig. 9.—Euphrasia Monroi. Surface view of upper epidermis above midrib. a, water-absorbing cell; b, stoma; c, excretory hair.

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Fig. 10.—Euphrasia Monroi. Transverse section of stem (× 230). a, epidermis; b, dead cortex; c, phloem; d, xylem; e, medullary ray; f, pith.

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Below these cells there is a basal cell which is small and has its wall cutinized.

Adjacent to these water-absorbing cells there are several layers of small, thin-walled cells which do not contain any chlorophyll.

Small vascular bundles end blindly in the small-celled tissue adjacent to the water-absorbing cells. The vascular bundles are numerous; both the xylem and the phloem contain parenchyma, and the bundle is surrounded by a sheath of thin-walled, colourless, parenchymatous cells.

On the upper surface, and especially above the midrib, there are a few excretory hairs which are covered with minute excrescences of calcium oxalate. These hairs are seen in surface view in fig. 9 and in transverse section in fig. 8.

Stem (fig. 10).—On the outside there is a bark formed of the dead epidermal and cortical cells. The cells of the cortex and of the epidermis have thickened walls, and the epidermal cells have their external walls cuticularized. A few of the epidermal cells are produced into short, stiff hairs with thick walls and a thin cuticle.

Bounding the bark there is a single layer of large cells with thin suberized walls: this is the endodermis. Inside this there is a pericycle: this is composed of 1–3 layers of small cells with thickened, lignified walls.

The phloem forms a wide band; the sieve-tubes are of small diameter; with the phloem there is a fair amount of parenchyma.

The xylem forms a wide ring; it is composed of wood-fibres and a few narrow vessels which have thickened walls and are very regularly arranged in rows.

The medullary rays are not very close together; they are uniseriate, and are composed of small cells with thickened lignified walls.

The pith is also lignified; the cells are rounded or polygonal, and have thin walls.

29. Wahlenbergia albomarginata Hook.

Habit.—The plant is a small perennial herb, 2–4 in. high with a branched rootstock putting up a few short, erect stems. The leaves are rosulate or crowded on the short stems; they are ¼—⅗ in. long, oblanceolate, obtuse, narrowed into a short petiole, entire, thick, and coriaceous; the margins are white and cartilaginous. The peduncles are leafless, one-flowered, and about 6 in. high.

Anatomy.

Leaf (fig. 11).—The upper epidermis consists of very large cells with thickened walls, especially the external ones. In addition there is a thin, rough cuticle. Some of the cells are produced into long, stiff hairs, the walls of which are very slightly cuticularized.

The lower epidermis is formed of small cells which have their external walls very much thickened. A cuticle is also present. Stomata are confined to the lower surface; the guard-cells are small, and are raised above the other epidermal cells. There are very small guard-cell ridges

The chlorenchyma is differentiated into palisade and spongy tissue. The palisade tissue consists of 3 rows of large, thin-walled cells which contain numerous fairly large chloroplasts. The two outer layers are closely packed, but there are small air-spaces between the cells in the third layer.

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The spongy tissue is composed of large, irregular, thin-wal ed cells which contain numerous chloroplasts; there are moderately large air-spaces between the cells.

In the margins of the leaf the epidermal cells are smaller, and their walls are very much thickened, and some of them are produced into small papillae. Inside this layer there is a group of small cells which have very thick mucilaginous walls and very small cell-cavities.

The vascular bundles are small and contain only a small amount of lignified tissue. There is no stereome. The bundle is surrounded by a sheath of thin-walled colourless cells. Below the midrib there are some small, round, thin-walled cells which do not contain chlorophyll: they are for water-storage.

Peduncle.—The epidermis is composed of small cells which have all their walls, especially the lateral ones, very much thickened. The cavities are small. In addition there is a fairly thick rough cuticle. Stomata are of the same type as in the leaf.

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Fig. 11.—Wahlenbergia albomarginata. Transverse section of leaf (× 48). a, unicellular hair; b, large cells of upper epidermis; c, cuticle; d, stereome in leaf-margin.

The cortex consists of 3–4 layers of oval cells with slightly thickened walls. These cells are closely arranged so that there are only very small air-spaces; the cells contain numerous chloroplasts. The endodermis is well marked, and consists of one layer of cells with thin suberized walls.

The phloem forms a narrow band. The sieve-tubes are of small diameter, and there is a good deal of parenchyma.

The amount of xylem is small. There are small groups of vessels surrounded by wood-fibres which have very thick walls and small cavities. The pith-cells are large and round; most of them are lignified, but there are a few cells in the centre which have unlignified walls.

Stem (fig. 12).—The epidermis is composed of somewhat larger cells than the epidermis of the peduncle; in transverse section the cells are squarish; their lateral walls are only slightly thickened, but the external

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and internal ones are much more so. There is a thick, rough cuticle. Some of the epidermal cells are produced into hairs like those on the leaf.

The cortex is a wider band than in the peduncle. The cells of the outermost layer have their walls slightly thickened, but the rest of the cortical cells have thin walls. There are only very small intercellular air-spaces. The cells contain a very few small chloroplasts in a peripheral layer of protoplasm. The cortex forms a water-storage tissue.

The endodermis and the phloem are the same as in the peduncle, except that the phloem is a wider zone of tissue. The cambium is easily seen.

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Fig. 12.—Wahlenbergia albomarginata. Transverse section of stem (× 48). a, unicellular hair; b, endodermis; c, phloem; d, cambium; e, xylem.

The xylem consists of vessels of small diameter; there is a large amount of xylem parenchyma. The pith is formed of large thin-walled cells which are closely packed together and are not lignified.

30. Celmisia longifolia Cass. var. gracilenta T. Kirk.

Habit.—This plant is a small, tufted, perennial herb. The leaves are all radical, simple, and erect; they are 3–7 in. long, 1½—1⅙ in. broad, and the margins are revolute. The whole leaf is covered with silvery-white tomentum, and is produced into a broad sheathing base, which is also covered with tomentum. The sheathing leaf-bases are persistent, and are used to store water (cf. with “tunic” grasses—e.g., Poa Colensoi).

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Anatomy.

Leaf (figs. 13–17).—The general shape of the leaf in transverse section is shown in fig. 13. From this it will be seen that the midrib is very prominent, that the tomentum is thick, and that the leaves are revolute almost to the margin.

Fig. 14 illustrates a section passing through the midrib. Both the lower and the upper epidermis consist of regular squarish cells which do not contain chlorophyll and which have their cell-walls very much thickened. There are no stomata in this region. From the epidermal layers very numerous fine hairs are produced, which form a silvery tomentum below the midrib and over the whole of the upper surface of the leaf. There is a thin cuticle on both surfaces of the leaf.

The vascular system in the midrib consists of one large bundle and two much smaller ones. The vessels of the xylem are arranged in very regular rows separated by xylem parenchyma. There is also a fairly large amount of parenchyma in the phloem. Above the phloem and below the xylem there is a mass of stereome, consisting of cells with very thick walls and small cavities. The cells above the xylem are larger than those below the phloem.

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Fig. 13.—Celmisia longifolia var. gracilenta. Transverse section of leaf (× 36). a, tomentum; b, vascular bundle.

Just above the lower epidermis there are 2 rows of chlorenchymatous cells. These cells are roundish, and have their walls slightly thickened, and contain numerous chloroplasts. Just below the main bundle these cells have their walls much thicker and contain a much smaller number of chloroplasts.

All the space between the upper epidermis and the chlorenchyma of the lower surface (except that occupied by the vascular bundles) is filled by a tissue consisting of very large cells with fairly thin walls. These cells are arranged very closely together, so that there are only minute intercellular air-spaces where three cells meet. All these cells form an aqueous tissue.

Section of the Leaf through the Lamina (fig. 15).—The upper epidermis consists of regular more or less squarish cells which are larger than the epidermal cells above the midrib. They have their walls considerably thickened, the external walls being thickened the most, and there is a

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rather thin, rough cuticle. From the upper surface there is produced a tomentum which is composed of very fine hairs. These hairs are 3–4 celled; the lowest cell has a cutinized wall.

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Fig. 14.—Celmisia longifolia var. gracilenta. Transverse section of leaf passing through midrib (× 175). a, upper epidermis; b, oil-drops; c, xylem; d, phloem; e, long multicellular hairs; f, shorter, more slender hairs; g, aqueous tissue.

The chlorenchyma is differentiated into palisade and spongy tissue. The palisade tissue consists of one layer of large, thin-walled cells, which contain numerous chloroplasts and also some large oil-globules. There are small intercellular air-spaces in this tissue.

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Fig. 15.—Celmisia longifolia var. gracilenta. Transverse section of lamina of leaf. a, upper epidermis; b, palisade parenchyma; c, oil-drops; d, spongy tissue; e, stoma; f, multicellular hair.
Fig. 16.—Celmisia longifolia var. gracilenta. Transverse section of sheathing leaf-base (× 36). a, tomentum; b, vascular bundle.

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The spongy tissue is composed of about 6 rows of cells. In the upper part of the leaf these cells are about the same length as breadth, but just above the lower epidermis they are narrower and are elongated in a direction parallel with the surface of the leaf. These cells also have thin walls and contain oil, which is more abundant nearer the upper than near the lower surface of the leaf.

The lower epidermis consists of cells which are oval in transverse section. Many of them are produced into long, stout, several-celled hairs which have thin walls. The lowest cell has a thin cuticle. These hairs

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Fig. 17.—Celmisia longifolia var. gracilenta. Transverse section of sheathing leaf-base (× 175). a, upper epidermis; b, hypoderma; c, mesophyll; d, stereome; e, xylem; f, phloem; g, multicellular hair.

are much longer and thicker than those of the upper surface (and those beneath the midrib), and they do not form such a dense mass, so that their form can be seen more easily.

Stomata are confined to the lower surface of the leaf, where they are numerous. As is often the case with leaves which have a dense tomentum, the stomata are raised above the epidermal cells. The guard-cells have very thick walls, and there are guard-cell ridges.

Sheathing Leaf-base (figs. 16 and 17).—Fig. 16 gives a schematic view of this; fig. 17 shows the structure in detail.

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Both the upper and the lower epidermis consist of very regular cells, the walls of which are only slightly thickened. On both surfaces there is a thin cuticle, and on the lower (the outer) surface there are a number of hairs like those on the lower surface of the leaf.

Beneath the upper epidermis there is a hypoderma which is composed of a single layer of small sclerized cells in which the walls are very thick and the lumen very small.

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Fig. 18.—Celmisia longifolia var. gracilenta. Transverse section of peduncle (× 230). a, multicellular hairs; b, ridged cuticle; c, unlignified cortex; d, lignified cortex; e, xylem; f, phloem.

The vascular bundles are of the same type as that described for the leaves, but the stereome above the xylem and below the phloem is formed of much smaller cells than in the leaf. All the mesophyll consists of aqueous tissue, which is composed of thin-walled, colourless cells. Near the lower surface there are 2 rows of these cells, which are regularly

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arranged, the inner layer consisting of much larger cells than the outer. These cells are roundish or squarish in section, but the rest of the cells of the aqueous tissue are very irregular in outline. They lie close together, so that the intercellular air-spaces are minute.

Peduncle (fig. 18).—The epidermis consists of somewhat irregular cells which have very thick walls, especially the external ones. From some of the epidermal cells there are produced long multicellular hairs like those on the under-surface of the leaf. A thin cuticle is present; its surface presents numerous very fine ridges.

Below the epidermis there is a zone of dead cortex, consisting of very irregular, thick-walled cells with brown contents. The rest of the ground-tissue of the stem consists of lignified tissue. This can be divided into two regions—

(1.)

An outer region where the vascular bundles are found. The cells in this region are rather small and have thick walls.

(2.)

An inner pith in which the cells have thin but lignified walls. These cells are large and roundish. Small intercellular air-spaces are found in this tissue. The stem is hollow.

The vascular bundles are small and quite separate from one another. There is parenchyma in both the phloem and the xylem. The scleren-chymatous cells around the bundles are small.

31. Olearia virgata Hook. f.

Habit.—This plant is an erect, much-branched shrub, 2–5 ft. high. The branches are spreading, tetragonous when young, almost terete in the older parts. The young branches are pubescent. The bark is dark red-brown. The leaves are opposite, obtuse, narrowed into a very short petiole, glabrous above and clothed with white tomentum beneath.

Anatomy.

Leaf (fig. 19).—The upper epidermis consists of medium-sized oblong cells; these have thin lateral and internal walls, but the external walls are thickened, and in addition there is a cuticle, which is, however, only a thin one. There are no stomata on the upper surface.

The lower epidermis is like the upper, but the external walls are not thickened, and many of the epidermal cells are produced into large T-shaped hairs, which are closely appressed to the surface.

The stomata are confined to the lower epidermis, and they are raised above the epidermal cells. The guard-cells are small and have thickened walls.

The chlorenchyma is differentiated. The palisade tissue consists of 2 rows of closely packed cells, the depth of which is only about one and a half times the breadth. The cells are thin-walled and contain numerous large chloroplasts.

The spongy tissue consists of 4 or 5 layers of irregular thin-walled cells with large air-spaces between them. These cells contain numerous chloroplasts, which are slightly smaller than those in the palisade tissue. The cells of the layer just above the lower epidermis are smaller and are more closely arranged.

The vascular bundle is small, and like that in Celmisia longifolia var. gracilenta except that there is no stereome. The vascular bundle is surrounded by a sheath of small, thin-walled, parenchymatous cells which contain a few chloroplasts arranged along their outside walls.

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Fig. 19.—Olearia virgata. a, upper epidermis; b, palisade parenchyma; c, spongy parenchyma; d, xylem; e, phloem; f, T-shaped hairs.
Fig. 20.—Olearia virgata. Transverse section of stem (× 36).
Fig. 21.—Olearia virgata. Transverse section of stem (× 175). a, sclerenchyma; b, corky cells; c, chlorenchyma; d, pericycle fibres; e, phloem; f, xylem; g, lignified pith.

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Stem (figs. 20 and 21).—The general arrangement of the tissues is shown diagrammatically in fig., 20. From this it will be seen that the stem is tetragonous and that in each of the corners there is a small mass of sclerenchyma. The structure of the stem is shown in detail in fig. 21.

On the outside there are dead epidermal cells with a thin cuticle, and below this there are a few dead cortical cells. Beneath this layer there are 2–4 layers of large, squarish cells which have their cell-walls both suberized and lignified. The portion of the cell-wall adjacent to the cell-cavity is suberized, and nearer the middle lamella it is lignified.

Inside this corky layer there is a zone of cortex. The cells of this tissue are more or less oval in transverse section, and are closely packed together so that the intercellular air-spaces are very small. These cells contain a small number of chloroplasts. At intervals there are groups of pericycle fibres. These are of small diameter and have thick walls. In the four corners of the stem there is a mass of sclerenchyma, which is composed of slightly larger cells than the pericycle fibres.

The phloem forms a continuous band with its elements rather regularly arranged. The xylem is composed for the greater part of wood-fibres which have thickened walls.

The medullary rays are not numerous; they are multiseriate (3 cells wide), and their cells have thickened, lignified walls.

The pith is composed of large round or polygonal cells, which have lignified, somewhat thickened, cell-walls.

32. Helichrysum bellidioides Hook. f.

Habit.—This plant is an herb. The stems are prostrate, slender, much branched, almost woody at the base, 6–12 in. long; the branches are numerous, erect, and leafy. The leaves are loosely imbricating, spreading, ¼—½ in. long, obovate-spathulate, apiculate, flat, one-nerved, with the upper surface glabrous and the lower clothed with cottony tomentum.

Anatomy.

Leaf.—The upper epidermis consists of regular, large cells, which have their inner and lateral walls thin and the external ones slightly thickened. There is a thin cuticle. A few of the cells are produced into hairs.

The lower epidermis consists of cells that are smaller than those of the upper epidermis. Their walls are thin, and there is a very thin cuticle. Many of these cells are produced into fine 2- or 3-celled hairs, which form a dense tomentum on the under-surface.

The chlorenchyma is differentiated into palisade and spongy tissue. The palisade tissue consists of 2 rows of cells with thin walls and numerous large chloroplasts; there are air-spaces between the cells.

The spongy tissue is composed of large, irregular, thin-walled cells, which contain abundant large chloroplasts. These cells form a rather loose tissue with large intercellular air-spaces.

Stomata are confined to the lower epidermis, and the guard-cells are raised (as in Celmisia longifolia var. gracilenta, Olearia virgata, and O. arborescens). The guard-cells are small.

The vascular bundle is small, and is surrounded by a sheath of thin-walled cells which contain a very few chloroplasts. Just above the xylem there is a small group of 8 or 10 sclerized cells. The amount of lignified tissue in the xylem is small; both xylem and phloem contain parenchyma.

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Between the bundle-sheath and the lower epidermis there are some thin-walled colourless cells which store water.

Stem.—The epidermis consists of squarish cells with their walls slightly thickened and with a thin cuticle. These cells contain tannin. Some of the epidermal cells are produced into hairs like those on the leaf.

The cortex consists of small regular cells; in the outer part of the cortex these cells have their walls lignified and also suberized. The inner layers of cortical tissue consist of thin-walled cells. All the cortical cells are closely packed together, so that there are only very small intercellular air-spaces. There is a well-marked endodermis, which consists of large cells with suberized walls.

The phloem forms a wide, continuous band; it contains a large amount of parenchyma.

The xylem forms a band about the same width as the phloem; it consists of vessels of rather small diameter and of wood-fibres.

The pith is solid, and consists of large, thin-walled polygonal cells which are closely arranged together. The pith-cells adjacent to the xylem are somewhat smaller and have their walls lignified.

33. Cassinia Vauvilliersii Hook. f. var. rubra Buch.

Habit.—This plant is an erect, closely branching shrub, 2–4 ft. high; the branches are stout, erect, and often glutinous. The leaves are numerous, close-set, erect or spreading, ¼—⅓ in. long, linear-obovate, narrowed into a short broad petiole, very coriaceous, clothed with hairs on both surfaces; the margins are slightly recurved.

Anatomy.

Leaf.—The upper epidermis consists of rather small cells which have slightly thickened walls. These cells contain a few small chloroplasts. There is a thick cuticle. Some of the epidermal cells are produced into long 3- or 4-celled hairs—2 or 3 small hairs at the base and a long cell at the end. There are no stomata on the upper surface.

The lower epidermal cells are smaller than the upper, and, like the latter, contain chloroplasts. Many of the cells are produced into hairs like those on the upper surface. The lower epidermal cells have slightly thickened walls, and there is also a thick cuticle.

The chlorenchyma is differentiated. The palisade tissue consists of 4 rows of large cells with slightly thickened walls and large chloroplasts. There are very small air-spaces between the cells.

The spongy parenchyma is composed of rather small, irregular cells which contain large chloroplasts. The walls are slightly thickened, and there are fairly large air-spaces between the cells.

Stomata are confined to the lower surface; they are of the same type as in Celmisia longifolia var. gracilenta.

The vascular bundles are small, and contain only a small amount of lignified tissue. They are surrounded by a sheath of thin-walled parenchymatous cells which contain only a small number of chloroplasts.

Stem.—The epidermis is composed of small cells which have thickened walls and also a fairly thick cuticle. Many of the cells are produced into hairs like those on the leaf.

Then there come some dead cortical cells; these have thick brown walls. Inside this layer there is suberized tissue, from 1 to 4 cells deep. The cells are large, thin-walled, and irregular.

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Below this tissue there are large groups of pericycle fibres; these have a small diameter, and their walls are thickened.

The phloem forms a wide band, with the sieve-tubes of small diameter; there is a fairly large amount of phloem parenchyma. The cambium is very easily seen.

The xylem contains vessels of fairly large diameter and wood-fibres which have very thick walls. There are no medullary rays.

The pith is solid; it consists of large roundish cells with thin walls.

34. Senecio bellidioides Hook. f.

Habit.—This is a small rosette plant. The leaves are all radical and spreading; the blades ¾—2½ in. long, broadly oblong, obtuse, rounded or slightly cordate at the base, membranous, with entire margins; the upper surface is more or less covered with stiff glandular hairs, and the lower is sparingly covered with tomentum. The petioles are about ¾ in. long, and are covered with hairs. The scapes are 1–12 in. high, branched, and pubescent.

Anatomy.

Leaf (figs. 22–26).—Fig. 22 gives a diagrammatic view of the transverse section of the leaf. From this it will be seen that the number of vascular bundles is small; the relative frequency of the different types is also seen in this diagram. Fig. 24 shows the structure of the midrib, and fig. 23 of the blade of the leaf.

The upper epidermis consists of rather small cells, the outer walls of which are slightly thickened. There is a thin cuticle present. Stomata are found on both surfaces; the guard-cells are level with the surface, and have thickened walls and small guard-cell ridges. Some of the upper epidermal cells are produced into hairs of two kinds—

(1.)

Capitate glandular hairs: These are very long, and are multicellular, and have a rounded head.

(2.)

There are also other multicellular hairs formed of about 9 cells. At the base there are about 7 small rectangular cells which are closely packed together and have their outer walls slightly cuticularized. Above these cells there is a large, wide, and shallow cell which has a thick but uncutinized wall. Beyond this cell there is an elongated one, also with a thickened, uncutinized wall.

The lower epidermis also consists of cells which are more or less oval in transverse section. They have thin walls, except for the external ones, which are slightly thickened. There is a thin cuticle. Stomata are present on this surface also. The epidermal cells contain a few chloroplasts. Some of the epidermal cells give rise to hairs of two kinds—

(1.)

There are a few glandular hairs as on the upper surface.

(2.)

Most of the hairs are like those on the upper surface, except that there are usually only 4 of the small cells and there are 2 long cells instead of 1.

The chlorenchyma is only slightly differentiated. The palisade tissue consists of 2 rows of cells, which have thin walls and contain numerous chloroplasts. These cells are wide and do not have the typical palisade form; they are fairly loosely arranged, so that there are large air-spaces between the cells.

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Fig. 22.—Senecio bellidioides. Transverse section of leaf (× 24). a, glandular hair; b, multicellular hair; c, vascular bundle.
Fig. 23.—Senecio bellidioides. Transverse section of leaf (× 110). a, glandular hair; b, multicellular hair; c, stoma; d, mesophyll.

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The spongy tissue consists of about 5 rows of large, irregular cells which have thin walls. There are fairly large air-spaces between the cells. The cells of the layer just above the lower epidermis are much smaller.

The Midrib.—There are three vascular bundles in the midrib. The lignified elements of the xylem are arranged regularly in rows which are

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Fig. 24.—Senecio bellidioides. Transverse section through midrib of leaf. a, multicellular hair; b, aqueous tissue; c, xylem; d, phloem; e, canal lined by epithelial layer; f, chlorenchyma; g, glandular hair.

separated by xylem parenchyma. There is a good deal of parenchyma with the phloem. Beneath the phloem of each bundle there are 1 or 2 large canals, which are lined by epithelial cells.

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Under the upper epidermis there are a few cells which have thickened walls, and above the lower epidermis there are 2 rows of roundish cells which contain chloroplasts and which have their walls slightly thickened.

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Fig. 25.—Senecio bellidiodes. Upper epidermis of leaf (× 36).
Fig. 26.—Senecio bellidioides. Lower epidermis of leaf (× 36).
Fig. 27.—Senecio bellidioides. Transverse section of scape (× 36)

The rest of the midrib is occupied by a mass of large, closely packed, thin-walled, more or less polygonal cells. These cells form a water-storage tissue.

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Figs. 25 and 26 show the surface view of the upper and lower faces of the leaf. From these it will be seen (1) that the glandular hairs are much more frequent on the upper surface, and (2) that most of the multicellular hairs of the lower epidermis are situated over the vascular bundles. This would suggest that they are for water-absorption.

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Fig. 28.—Senecio bellidioides. Transverse section of scape (× 175). a, multicellular hair; b, glandular hair; c, chlorenchyma; d, lignified tissue; e, vascular bundle; f, pith.

Scape (figs. 27 and 28).—The structure of the scape is shown schematically in fig. 27 and in detail in fig. 28.

The epidermis consists of fairly large cells which have thickened walls. A thin, ridged cuticle is present. Stomata are present, but they are not numerous. They are of the same type as those in the leaf. There are two kinds of hairs—(1) glandular; (2) hairs like those described for the upper epidermis, but the large cell at the base of the elongated cell is not present.

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The chlorenchyma consists of about 5 rows of large, roundish cells which have thin walls and numerous chloroplasts. There are moderately large air-spaces in this tissue.

Then there comes a band of smaller, roundish cells which have thickened, lignified walls. Below this there is the phloem, which is a narrow band of tissue. The xylem contains parenchymatous cells.

35. Gahnia procera Forst.

Habit.—This is a perennial tufted herb. The stems are about 2 ft. high, and are stout. The leaves are as long as or slightly longer than the stems, and are narrowed into long filiform points; the margins are involute, smooth above and scabrid below; the sheaths are dark brown or almost black.

Anatomy.

Leaf (figs. 2932).—The transverse section of this is shown diagram-matically in fig. 29. This shows that the leaf is involute and furrowed, and that under each ridge there is a vascular bundle, accompanied by an extensive development of sclerenchyma. The margin of the leaf is occupied by a mass of sclerenchyma. Figs. 30–32 show the structure of the leaf in more detail.

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Fig. 29.—Gahnia procera. Transverse section of leaf (× 36). a, chlorenchyma; b, sclerenchyma; c, vascular bundles.
Fig. 33.—Gahnia procera. Transverse section of stem (× 24). a, sclerenchyma; b, vascular bundles.

The upper epidermis consists of small cells, which taper slightly towards the outside of the leaf. The walls of these cells are thickened, especially the external walls, which produce small papillae. There is no cuticle.

The lower epidermis consists of very regular oval cells, which have their cell-walls, especially the external ones, thickened. There is a thin cuticle on the lower surface.

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Fig. 30.—Gahnia procera. Transverse section of leaf (× 230), a, upper epidermis; b, hypoderma; c, mesophyll; d, pulvinus; e, xylem; f, phloem; g, sclerenchyma.
Fig. 31.—Gahnia procera. Lower epidermis of leaf, at margin (× 230) a, stiff, unicellular hair.
Fig. 32.—Gahnia procera. Transverse section of margin of leaf (× 230) a, hair; b, sclerenchyma.

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Stomata are confined to the upper surface, where they are found only in the furrows. They are sunken below the level of the epidermal cells, and the guard-cells are small and have very thick cell-walls. The epidermal cells in the furrow are somewhat pear-shaped, and their walls are irregularly thickened, the result being a number of short papillae which serve to protect the stomata.

At the base of each furrow there are 3–5 large cells, which form a pulvinus. The cells of the pulvinus have a very thin cuticle, but the other epidermal cells are not cuticularized.

The chlorenchyma is not differentiated into palisade and spongy tissue. The cells of this tissue are small, more or less polygonal, and very closely packed together. They contain a small number of fairly large chloroplasts: Some of the cells of this tissue contain tannin.

Below the upper epidermis, in the ridges, there is a hypoderma of very small lignified cells, in which the walls are very thick, so that the lumen is very small. In the middle of the ridge these sclerenchymatous cells are continued downwards, forming a band several cells wide, and then forming a sheath above the upper part of the vascular bundle.

The vascular bundle is surrounded by a sheath of oval lignified cells the inner cell-walls of which are thicker than the outer. The vascular bundle is of the usual monocotyledonous type, and has all the xylem parenchyma lignified.

Below the vascular bundle there is another zone of sclerenchyma, this being continued as a layer from 1 to 5 cells thick above the lower epidermis and below the chlorenchyma. These cells are small and have very small cell-cavities.

On the upper portion of the leaf there are small, stiff hairs on the lower surface and on the margins of the leaf. These are shown in figs. 31 and 32. They are very stiff, unicellular hairs with very thick stratified cell-walls, and are formed from the epidermal cells.

Peduncle.—This is shown diagrammatically in figure 33 (p. 301). The stem is hollow, and all the tissues except the epidermis and the phloem are lignified. This diagram shows the irregular arrangement of the vascular bundles, each of which is surrounded by-sclerenchyma.

Fig. 34 gives a more detailed view of part of the stem.

The epidermis consists of small pear-shaped cells with thickened cell-walls. A fairly thick cuticle is present.

Beneath the epidermis there is a more or less regular circle of vascular bundles, each of which is surrounded by a large mass of sclerenchyma, consisting of small cells with very thick cell-walls.

As we pass inwards the bundles become larger, and the amount of sclerenchyma around them is not so great. The cells of the sclerenchyma are somewhat larger and have larger cell-cavities.

The ground-tissue consists of fairly large, more or less regular cells, the walls of which are only slightly thickened and are lignified. These cells are closely arranged, so that there are only very small intercellular air-spaces. The cortical cells near the middle of the stem are somewhat larger, and the cell-walls are thinner.

Bounding the ground-tissue there is a zone of cells which are very irregular both in shape and in size. These cells are empty and their walls are suberized.

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Fig. 34.—Gahnia procera. Transverse section of stem (× 150). a, cuticle; b, sclerenchyma; c, xylem; d, phloem.

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36. Astelia montana (T. Kirk) Cockayne.

Habit.—This is a stout, densely tufted, perennial herb. The leaves are numerous, spreading, 1–2 ft. long and ½–¾ in. broad, linear-lanceolate and acuminate. The leaves are very tough and leathery, and are many-veined; one nerve on each side is more prominent than the rest, and the margins and midrib are often coloured a yellow-red. Both the upper and the lower faces of the leaf are clothed with white tomentum. The base of the leaf is sheathing; and is densely covered with long silky hairs.

Anatomy.

Leaf.—Fig. 35 gives diagrammatically a view of a transverse section of half the leaf. From this it will be seen that there are two veins much more prominent than the others, and also more prominent than the midrib. Fig. 36 shows a transverse section through the midrib, and fig. 37 through one of the prominent veins.

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Fig. 35.—Astelia montana. Transverse section of leaf (× 9). a, tomentum; b, aqueous tissue; c, stereome; d, vascular bundle; e, chlorenchyma.

Section through Midrib.—Both the upper and the lower epidermis consist of large cells somewhat elongated in a direction at right angles to the surface of the leaf. Above and below the veins the epidermal cells are more or less squarish. The epidermal cells have their walls, especially the external ones, thickened, and there is a cuticle present on both surfaces.

At intervals on both surfaces the epidermis is interrupted by groups of peculiarly modified cells forming a kind of scale. The scale consists of a short stalk of thin-walled cells, and above this the cells are larger and have thickened, cutinized walls. The cuticle of the uppermost tier of cells is frayed out into a kind of tomentum which more or less covers the surface of the leaf. The whole apparatus appears to be a modification for water-absorption.

Below the upper epidermis there is a zone of aqueous tissue, consisting of about 4 rows of very large, regularly arranged, closely packed, rectangular cells, which do not contain chloroplasts, and which have thickened, mucilaginous cell-walls.

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The chlorenchyma is not differentiated into spongy and palisade tissue. It consists of closely packed polygonal or roundish cells which contain numerous chloroplasts. There are no intercellular air-spaces.

Stomata are found on the lower surface only. The guard-cells are sunken below the surface of the epidermis, and the stomata are further protected by small guard-cell ridges over the opening. Subsidiary cells are present.

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Fig. 36.—Astelia montana. Transverse section through midrib (× 175).a, tomentum; b, upper epidermis; c, aqueous tissue; d, mesophyll; e, stoma; f, hair; g, stereome.

The vascular bundle is surrounded by a large mass of sclerenchyma: these cells are irregular and very closely packed, and have fairly thick cell-walls. The xylem and the phloem have the cell-walls of all the paren-chymatous cells lignified. The layer of mesophyll cells adjacent to the sclerenchyma is devoid of chloroplasts.

– 307 –

Section through the Lamina in the Region of a Prominent Vein (fig. 37)—In these veins there is a large, more or less T-shaped mass of sclerenchyma surrounding the vascular bundle. As in the midrib, these cells are smaller on the under side than on the upper side, but here those on the upper surface are much larger than those above the midrib.

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Fig. 37.—Astelia montana. Section through one of large veins (× 175). a, tomentum; b, upper epidermis; c, aqueous tissue; d, mesophyll; e, stoma; f, hair; g, stereome.

Between the sclerenchyma and the upper epidermis there is a hypoderma of aqueous tissue consisting of more or less oval cells. Between the sclerenchyma and the lower epidermis this layer is only one cell thick.

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As we pass away from the midrib the aqueous tissue consists of rounded or polygonal cells which are not arranged in the definite rows found near the midrib.

37. Dianella intermedia Endl.

Habit.—This plant is a perennial herb, bearing numerous leaves, which are crowded at the base of the stem. The leaves are linear, 1–1½ ft. long, ½ in. wide, and are arranged in two vertical rows (distichous); the bases of the leaves are sheathing. The margins and the midrib are coloured orange-red.

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Fig. 38.—Dianella intermedia. Transverse section of leaf (× 24). a, cuticle; b, stereome; c, vascular bundle; d, aqueous tissue.
Fig. 39.—Dianella intermedia. Transverse section through midrib of leaf (× 175). a, cuticle of upper surface; b, aqueous tissue; c, chlorenchyma; d, cuticle of lower surface; e, stoma; f, stereome; g, xylem; h, phloem.

Anatomy.

Leaf (figs. 3843).— Fig. 38 shows the general arrangement of the tissues in a transverse section of the leaf. The vascular bundles are surrounded by a large band of sclerenchyma, which traverses the whole width of the leaf. Under the upper epidermis are some lignified cells, and in the centre of each mass of chlorenchyma there is some aqueous tissue. Fig. 39 shows in more detail the structure at the midrib.

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The upper epidermis consists of rather irregular cells with thickened cell-walls. A thick cuticle is also present.

Below the epidermis there are 2 rows of large cells with thickened, somewhat mucilaginous cell-walls. These do not contain chloroplasts, and they form an aqueous tissue.

The chlorenchyma is not differentiated into palisade and spongy parenchyma. It consists of rounded or polygonal cells which contain numerous chloroplasts.

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Fig. 40.—Dianella intermedia. Transverse section through lamina of leaf (× 175). a, cuticle; b, hypoderma; c, stereome; d, lignified sheath; e, chlorenchyma; f, aqueous tissue; g, xylem; h, phloem.

The lower epidermis is formed of roundish or oval cells. There is a thick cuticle on this surface also.

The stomata are confined to the lower surface, and are found in the slight grooves. The guard-cells are small, and are deeply sunken below the surface, and the opening is protected by projections of the cuticle. All the epidermal cells in the grooves have curious peg-like cuticular projections, so that a surface view presents a peculiar appearance. These are shown in surface view in fig. 42, and in transverse section in fig. 43.

Fig. 40 gives a transverse section through the lamina, not passing through the midrib. The cuticle is much thicker than above the midrib. The upper epidermis consists of regular oblong cells, which are a little larger above the sclerenchyma.

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Below this there is a hypoderma, from 1 to 4 cells deep, which consists of regular cells with lignified walls. Above the sclerenchyma bands this layer is only 1 cell thick, but above the chlorenchyma 2–3.

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Fig. 41.—Dianella intermedia. Transverse section of margin of leaf (× 260). a, cuticle; b, sclerenchyma.
Fig. 42.—Dianella intermedia Surface view of epidermis of lower surface (× 260). a, opening above stomata.
Fig. 43.—Dianella intermedia. a, guard-cells; b, cuticle.

The sclerenchyma consists of irregular cells with small cavities. Near the upper surface of the leaf these cells are much larger than they are near the lower surface.

The band of lignified cells beneath the upper epidermis is continued down beside each band of sclererchyma. Here it is 2 cells wide, and consists of oval cells.

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The chlorenchyma forms a compact mass, and in the centre of it there is some aqueous tissue which consists of very large roundish cells with very thin cell-walls.

Fig. 41 shows a transverse section of the margin of the leaf. The cuticle is very thick. The cells of the upper epidermis are slightly elongated at right angles to the surface of the leaf, and have thickened walls, and the cells of the lower epidermis are smaller and are squarish. Beneath the epidermis there is a hypoderma composed of 1 or 2 layers of cells with thickened, lignified cell-walls. The rest of the margin is occupied by a large mass of sclerenchyma, the cells of which have their lumen almost obliterated.

38. Libertia ixioides Spreng.

Habit.—A perennial herb with a short creeping rhizome and long fibrous roots. The leaves are numerous, densely crowded, linear, flat, rigid, and arranged in two vertical series (distichous). The margins are cartilaginous and smooth.

Anatomy.

Leaf (figs. 44–47).—Fig. 44 shows diagrammatically a view of half the transverse section of the leaf. From this it will be seen that the vascular bundles are arranged in two series, one along each face of the leaf; that the bundles are opposite, and that each is surrounded by a mass of sclerenchyma.

Figs. 45 and 46 show in more detail the structure in transverse section.

The epidermis is composed of small, squarish cells, all the walls of which are thickened, and there is also a thick cuticle.

Stomata are found on both surfaces, and they are fairly frequent. The guard-cells are sunken right below the epidermis, and they have thickened cell-walls. The stoma is therefore at the bottom of a pit.

The chlorenchyma consists of large, roundish cells with somewhat thickened cell-walls and containing numerous chloroplasts. This tissue is fairly compact, so that there are only small intercellular air-spaces. Beneath each stoma, however, there is a fair-sized air-space.

The vascular bundles are of the usual monocotyledonous type, and all the xylem elements are lignified. Surrounding each vascular bundle there is a mass of sclerenchyma; this is composed of small roundish cells with thick cell-walls.

The central part of the leaf is occupied by a colourless tissue formed of large cells with slightly thickened cell-walls, and with small air-spaces between the cells. This tissue forms an aqueous tissue. In some parts the cells lying between the two opposite masses of sclerenchyma have lignified cell-walls.

Fig. 46 shows a transverse section through the margin of the leaf, which is thickened. The cuticle here is thicker, and the epidermal cells are somewhat larger, and their external cell-walls are thicker than near the centre of the leaf. Under the epidermis there is a single layer of cells which contain a few chloroplasts. The rest of the space is occupied by a large mass of sclerenchyma, composed of cells with a very small lumen. In the centre of this mass there is a small vascular bundle.

Peduncle (fig. 48).—The epidermis is composed of small cells with all their walls, and especially the lateral walls, very much thickened. A cuticle is present, but it is not so thick as in the leaf.

Stomata are not frequent; the guard-cells have thickened cell-walls and are but slightly sunken, so that they are not at the bottom of a pit as in the leaf.

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Fig. 44.—Libertia ixioides. Transverse section of leaf (× 54). a, sclerenchyma; b, chlorenchyma; c, vascular bundle; d, aqueous tissue.
Fig. 46.—Libertia ixioides. Transverse section of margin of leaf (× 230). a, cuticle; b, sclerenchyma; c, vascular bundle.
Fig. 47.—Libertia ixioides. Surface view of epidermis (× 230). a, opening above stoma.

– 313 –

Beneath the epidermis there is some chlorenchyma—a band 2–4 cells deep, composed of spherical cells very closely arranged together, so that there are only minute air-spaces.

There are 4 more or less regular concentric rings of vascular bundles, the outer ones of which are composed of small bundles. The vascular bundles are of the usual monocotyledonous type, and each is surrounded by a small amount of sclerenchyma.

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Fig. 45.—Libertia ixioides. Transverse section of leaf (× 230). a, cuticle; b, stoma; c, sclerenchyma; d, phloem; e, xylem; f, aqueous tissue; g, chlorenchyma.

All the cells of the ground-tissue except the chlorophyll-containing cells have pitted lignified walls. The cells nearest the chlorenchyma are small, have thick walls; and are closely arranged, so that there are no intercellular air-spaces. As we pass towards the centre of the stem the cells become larger and rounder, and their walls are thinner, and there are larger intercellular air-spaces.

– 314 –
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Fig. 48.—Libertia ixioides. Transverse section of peduncle (× 230). a, cuticle; b, stoma; c, chlorenchyma; d, sclerenchyma; e, phloem; f, xylem; g, pitted walls.