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The Journal of Indian Botany/Volume 1/November 1919/The Physiological Anatomy of the Plants of The Indian Desert

THE

Journal of Indian Botany.

Vol. I. NOVEMBER, 1919. No. 3.

THE PHYSIOLOGICAL ANATOMY OF THE PLANTS OF THE INDIAN DESERT

BY

T. S. Sabnis, B.A., B.Sc.

St. Xavier's College, Bombay.

{Continued from last issue.)


Cleome brachycarpa Vahl. Figs. 13, 14, 19, 20, 21. Herbaceous. Front cavity of stomata on a level with the surface. Guard-cells a little above the plane of the surrounding cells. Mesophyll isobilateral. Some of the palisade cells with tanniniferous contents. Middle tissue of the mesophyll formed of large colourless parenchymatous cells. Veins provided with colourless sheaths. Glandular hairs multicellular and capitate. Outer walls of the epidermal cells of the axis granulated. Axis ribbed. Pericycle formed of large thin groups of stone-cells. Assimilatory tissue in the axis consisting of chlorenchyma. Wood composite. Soft bast forming a continuous ring. Pith formed of thin-walled cells.

Cleome viscosa L. Figs. 15, 16, 28. Herbaceous. Epidermis of the leaf formed of thin-walled cells. Guard-cells elevated a little above the plane of the surrounding cells. Front cavity of the stomata in a level with the surface. Mesophyll formed of palisade tissue on the adaxial side and of arm-palisade tissue on the abaxial side. Internal glands absent. Glandular hairs multicellular and capitate. Veins not provided with sheaths. Stone-cell groups of the pericycle triangular. Assimilatory tissue of the axis formed of chlorenchyma. Wood composite. Soft bast forming groups. Pith formed of thin-walled cells.

Gynandropsis pentaphylla DC. Figs. 22, 23, 24, 25, 26, 29. Herbaceous. Guard-cells a little elevated above the plane of the surrounding cells. Mesophyll formed of palisade tissue on the adaxial side and of spongy tissue on the abaxial side. Internal glands absent, Veins provided with green sheaths. Glandular hairs multicellular and capitate. Epidermis of the axis two-layered. Pericycle formed of rhomboidal stone-cell groups. Wood composite. Soft bast forming a continuous ring. Pith formed of thin-walled cells.

Cadaba indica Lam. Figs. 30, 31, 32, 33, 34, 35. Woody. Outer walls of the epidermal cells of the leaf greatly thickened and papillose. Guard-cells in the plane of the surrounding cells. Mesophyll formed wholly of short palisade cells. Internal glands in the leaf in the form of parenchymatous cells with tanniniferous contents. Veins not provided with sheaths. Water-storing tracheids occurring at the terminations of the veins. Clothing hairs peltate. Glandular hairs absent. Outer walls of the epidermal cells of the axis superficially granulated and lateral walls thickened. Pericycle formed of rhomboidal groups of stone-cells. Wood forming a composite ring; soft bast forming a continuous ring.

Capparis decidua Pax. Figs. 27, 36, 37. Woody. Leaves occurring only on young shoots. Epidermis of the leaf and axis formed of vertically elongated highly thick-walled cells. Mesophyll isobilateral with an extensive middle tissue of parechymatous cells. Internal glands in the form of numerous cells with tanniniferous contents. Veins not provided with sheaths. Pits present in the epidermis of the axis. Assimilatory tissue in the axis formed of palisade cells. A ring, 1-2 cell thick, of sclereids occurring below the assimilatory tissue. Pericycle formed of rhomboidal groups of stone-cells. Wood formed of xylem bundles connected by strands of interfascicular wood-prosenchyma. Soft bast forming groups. Pith composed of thin-walled cells.

Structure of the Leaf

Epidermis.—Outer walls are thickened and somewhat papillose in all members except Cleome viscosa (fig. 16.) The thickening and papillose differentiation is considerable in Cleome papillosa (fig. 11), Cadaba indica (fig. 30), Gynandropsis pentaphylla (fig. 22) and Capparis decidua. Lateral walls are thin in all the numbers except Capparis decidua, where they are thickned; they are somewhat undulate in all the members. Epidermal cells at the margin are rounded forming the marginal epidermis compact and rigid. Some of the lower epidermal cells in Cleome brachycarpa are larger and longer than broad, perhaps serving as water-reservoirs. Epidermal cells at the margin and along the mid-rib are smaller than in the other part of the leaf blade.

Stomata are surrounded by four to six ordinary epidermal cells (fig. 19) and are more numerous on the under surface. They are placed in depressions formed by the outer thickened and papillose walls of the epidermal cells in Cleome papillosa (fig. 11), Cadaba indica (figs. 30, 31) and Capparis decidua, the guard-cells being situated in the plane of the surrounding cells. In the other members the guard-cells are elevated above the plane of the surrounding cells, so that the front cavity is on a level with the surface (figs. 23, 27.).

The mesophyll is composed of palisade tissue on the adaxial side in all the members and on the abaxial side of arm-palisade tissue in Cleome viscosa (fig. 16) or of spongy tissue in Gynandropsis pentaphtylla (fig. 22). The mesophyll is isobilateral and is composed wholly of short palisade cells in Cadaba indica (fig. 30) or composed of palisade tissue on either side with a middle tissue of thin-walled colourless parenchymatous cells in Cleome brachycarpa (fig. 14) and Capparis decidua. The middle tissue in the former partakes in the formation of bundle-sheaths; and in the latter it is very extensive and forms perhaps a water-storage tissue. Internal secretory organs are of the nature of myrosin cells and are represented by (a) palisade like cells occurring in small groups on both sides below the epidermis in Cleome viscosa or (b) by parenchymatous cells in the middle tissue in Cadaba indica (fig. 30) and in Capparis decidua commonly occurring near the veins and quite numerous above the bundle of the mid-rib. The veins are embedded in all the members. They are provided with a sheath either of large colourless parenchymatous cells or of distinct green parenchymatous cells in Cleome brachycarpa (fig. 14) and Gynandropsis pentaphylla (fig. 22) respectively. Groups of large water-storing tracheids occur at the terminations of the veins in Cadaba indica (fig. 30 W). The vascular bundles of the mid-rib are arranged in the form of an arc with collenchyma on the lower side extending to the epidermis. The mid-rib projects on the lower side.

The hairy covering of the leaf and axis consists of (a) clothing and (b) glandular hairs.

(a) Clothing hairs are not unicellular in any of the members. Cleome papillosa and Cleome brachycarpa have shaggy hairs, the cells of which end superficially in sharp spiny apices (figs. 10, 11, 12). In Cadaba indica there are peltate hairs composed of a uniseriate stalk, much longer on the axis, and of a circular shield which in surface view presents a notched margin (fig. 33). Hairs are more numerous on the lower side of the leaf and especially on the mid-rib.

(b) Glandular hairs are present on the leaf and axis in all members except Cadaba indica. They are composed of a multicellular head irregularly divided (figs. 11, 13, 18). They are not numerous either on the leaf or axis; they are however more common on the margin of the leaf. They are numerous and longer on the axis than on the leaf (fig. 26). In Cleome brachycarpa there are a few multicellular glandular hairs with a spiny curved apex (fig. 20).

Structure of the Axis

Epidermis consists of small cells with outer and inner walls thickened. Lateral walls are also thickened in Cleome papillosa and Cadaba indica. Epidermis is two-layered in Gynandropsis pentaphylla. Outer walls are superficially granulated in species of Cleome. Epidermis of Capparis decidua consists of vertically elongated small cells with outer walls greatly thickened and cuticularised. Epidermis of Capparis decidua is characterised by numerous small pits which in T. S. are bounded laterally by two ordinary epidermal cells and beneath by a curved cell. Viewed from the surface the pits resemble small square holes bounded by 4-5 cells. These pits may possess the function of stomata without any regulating apparatus. The axis of Cleome brachycarpa and Cleome viscosa is ribbed, the ribs being strengthened by collenchyma. In Cleome brachycarpa there are some large cells intercalated among the small epidermal cells of the ribs with perhaps partly a water-absorbing and partly a strengthening function.

The stomata are surrounded by 4-6 ordinary epidermal cells as seen in surface view. The front cavity is placed in a depression produced by the outer thickened epidermal walls. The guard-cells are in the plane of the surrounding cells. Stomata are replaced by pits in Capparis decidua, as described already.

Primary cortex is characterised by an assimilatory tissue composed of chlorenchyma, except in Capparis decidua where it is replaced by the palisade tissue. In Capparis decidua there are sclereids in a ring below the assimilatory tissue. The sclereids have thickened and radially striated walls and are characterised by pitted markings.

The pericycle is represented by groups of stone-cells, either thin and long as in Cleome brachycarpa and Cleome papillosa, or triangular as in Cleome viscosa or rhomboidal as in other species.

The structure of the wood can be seen from the following table. (p. 71.)

The soft bast forms a continuous ring as in Cleome brachycarpa, Cadaba indica and Gynandropsis pentaphylla, or forms groups as in other members.

The pith is either composed of thin-walled cells as in Cleome

brachycarpa, Cleome viscosa and Gynandropsis pentaphylla, or of thick-walled cells, as in other species.

General Review: — Outer walls of the epidermal cells are thickened. Guard-cells are accompanied by ordinary 4-6 epidermal cells and are usually elevated above the plane of the surrounding cells. The mesophyll is either composed wholly of palisade tissue or is isobilateral, or is composed of palisade tissue on the adaxial side and of arm-palisade tissue or spongy tissue on the abaxial side. Internal secretory cells with tanniniferous contents are usually present in the leaf. The veins are embedded and are in some species provided with bundle-sheaths. Water-storing tracheids occur in the leaf and axis in some species. Mutlicellular capitate glandular hairs are of common occurrence. Peltate clothing hairs are present in Caclaba inclica. Primary cortex is characterised by an assimilatory tissue composed either of chloren- chyma or of palisade tissue. The pericycle is composed of groups of stone-cells. The structure of the wood is composite. The soft bast forms a continuous ring or occurs in groups. The pith is composed either of thin-walled or of thick-walled cells.

VIOLACEAE.

Viola Stocksii Boiss. — Epidermal cells of the leaf and axis with inner walls gelatinised and with outer walls thickened and muriculate. Palisade-like elongation of the epidermal cells character- istic of the axis. Stomata present on both the surfaces. Guard-cells elevated above the plane of the surrounding cells. Mesophyll formed of palisade tissue on the adaxial side and of arm-palisade tissue on the abaxial side. Internal secretory organs absent. Oxalate of lime in the form of large clustered crystals in the leaf. Veins embedded and not provided with bundle-sheaths. Hairy covering absent. Scleren- chymatous pericycle absent. Wood composite. Vessels small and arranged in numerous complete rows. Medullary rays uniseriate Collenchyma occurring at the inner margin of the wood. Pith composed of thin-walled cells.

Structure of the Leaf : — The epidermis is composed of tabular cells, with outer walls thickened, muriculate and convexly arched outwards, and with inner walls gelatinised. Lateral walls are wavy. The marginal epidermal cells have outer as well as inner^walls thick- ened. The gelatinised inner walls of the epidermis can absorb and retain water. The epidermis thus forms a kind of water-storing tissue. Stomata occur on both the surfaces. Guard-cells are elevated and are accompanied by subsidiary cells. The front cavity is on a level with the surface. The mesophyll is composed of palisade tissue on the adaxial side and of arm-palisade tissue on the abaxial side. Internal secretory organs do not occur either in the leaf or axis. Numerous large clustered crystals of oxalate of lirne occur in the arm-palisade tissue of the mesophyll. The crystals are wanting in the axis. The veins are embeded and are not provided with bundle- sheaths.

Both the leaf and the axis are devoid of hairs. The absence of hairs is compensated for by the gelatinisation of the inner walls of the epidermal cells.

Structure of the Axis : — Epidermis consists mostly of tabular cells with outer walls thickened, muriculate and convexly arched outwards- The inner walls are gelatinised and the lateral walls are straight. The epidermis is distinguished by two common features (l) palisade- like elongation of the epidermal cells in some parts (2) gelatinisation of the inner walls of the epidermal cells which are sometimes characterised by thin dividing walls parallel to the surface beneath which mucilage is found. The epidermis may occasionally serve as a water-storing tissue on account of these two features.

Cells of the outermost layer of the cortex show collenchymatous differentiation at their outer angles. The cortex is distinguished by the occurrence of cortical vascular bundles in the cortical chlorophyll containing parenchyma.

Sclerenchymatous pericycle is absent. The structure of the wood is composite. The vessels are small and are arranged almost in numerous complete rows. Interfascicular wood-prosenchyma is little developed. Medullary rays are uniserate and numerous. Small- celled collenchyma occurs at the inner margin of the wood. Soft bast forms a continuous ring.

The pith consist of thin-walled cells.

POLYGALACEAE.

Polygala erioptera DC. —Figs. 38, 39. Leaf and axis.— Numer- ous lysigenous cavities in the lower half of the mesophyll. Clustered crystals occurring near the veins. Compact bundles, comb-like at their ends, of diamond shaped bodies in the palisade-like cells in the upper half of the mesophyll. Epidermis of the axis two- layered. Axis ribbed. Eibs strengthened by stone- cell groups. Assimilatory tissue of the axis formed of palisade tissue. Scler- enchymatous pericycle in the form of groups of thick-walled and stratified bast fibres with small lumen.

Polygala irregularis Boiss.— Figs. 40, 41. Axis only.— Axis ribbed, groups of stone-cells strengthening the ribs. Epidermis one-layered. Assimilatory tissue composed of chlorenchyma. Aque- ous cells between the groups of bast fibres. Sclerenchymatous pericycle forming a loose ring of bast fibres. Oxalate of lime not occurring in any form.

Structure of the Leaf : — Epidermis in P. erioptera consists of tabular cells with outer and inner walls arched convexly outwards and inwards respectively. Outer walls are thickened ; lateral walls are thin and straight.

Stomata occur on both the surfaces of the leaf. The guard-cells are surrounded by ordinary epidermal cells and are situated in the plane of the surrounding cells (figs. 38, 41). The front cavity is arched over by outer horns of the guard-cells, which are quite pro- minent and come close together. The front cavity is placed in a depression formed by the outer thickened walls of the epidermal cells. Stomata on the axis (fig. 41) of both the species have the same characters as those on the leaf of P. erioptera. The mesophyll is composed of the palisade tissue on the upper side and of arm- palisade tissue on the lower. There are numerous lysigenously formed cavities in the arm-palisade tissue (fig. 38 L.C.) ; they may occasionally serve for storing water.

Oxalate of lime occurs in the form of clustered crystals near the veins of the leaves and in the assimilatory tissue of the axis of P. erioptera (figs. 38, 39). Besides the clustered crystals, there are elongated compact bundles of diamond shaped bodies, in the palisade tissue of the leaf ; these bundles are comb-like at their ends on account of the projecting pointed ends of the diamond shaped bodies. As regards composition of these bodies, I cannot say anything. Oxalate of lime is not found in any form in P. irregularis.

Veins are few and are embedded ; they are enclosed in bundle* sheaths of thin-walled colourless cells.

Hairy covering on the leaf and axis in both the species consists of unicellular thin-walled clothing hairs, either straight or hooked, and distinguished by knob-like thickenings on their walls. Glandular hairs are not found.

Structure of the Axis : — Epidermis is two-layered in P. erioptera while it is single layered in P. irregularis. Epidermal cells are tabular with outer-walls greatly thickened. Outer walls are convexly arched outwards in P. irregularis. Cuticle is thick, especially so in P. eriop- tera. Lateral walls are straight. The primary cortex functions as the assimilatory tissue and is composed of chlorophyll containing parenchyma in P. irregularis and of palisade tissue in P. erioptera. Groups of stone-cells occur in the ribs.

The pericycle is composed of a more or less continuous ring of bast-fibres, which are thickened, straitified and have a narrow lumen In P. erioptera. The ring is of uniform breadth in P. erioptera, while in P. irregularis it is single layered on a small portion on one side, indicating the prostrate or inclined nature of the axis, sclerenchy- matcus pericycle being least developed on the lower side of the axis. There are thin-walled colourless cells between and on either side of some of the groups of bast-fibres in P. irregularis ; they may occasionally serve as acqueous cells.

The wood is composite with vessels uniformly distributed in the interfascicular wood-prosenchyma. In P. irregularis the vascular ring is narrowed on the side where the sclerenchymatous pericycle is reduced ; there are very few vessels in this portion which is mostly occupied by interfascicular wood-prosenchyma. This may be ac- counted for by the fact of less vigorous functional activity on the lower side of the prostrate or inclined axis of P. irregularis. Vessels are large and few and are arranged in incomplete rows. Medullary rays are usually uniseriate and numerous.

The pith is composed of very thin-walled cells.

CARYOPHYLLACEAE.

Polycarpaea corymbosa Lam. — Figs. 42, 43, 44. Epidermal cells of the leaves with outer walls thickened and papillose. Guard-cells accompanied by subsidiary cells. The front cavity greatly depressed in the axis. Mesophyll isobilateral. Abundance of cells with tannini- ferous contents characteristic of the leaf and axis. Oxalate of lime in the form of clustered crystals. Assimilatory tissue in the axis formed of chlorenchyma. Pericycle composed of large groups of stone cells with a sclerenchymatous tissue on its outer side. Wood composed of large xylem bundles separated by strands of tissue, resembling medullary rays, continuous with the outer sclerenchyma. Large water-storing tracheids with reticulate markings in the xylem bundles near the medullary-ray-like strands. Pith formed of thick- walled cells.

Structure of the Leaf : — The epidermis consists of polygonal cells with outer walls thickened and papillose (tig. 42). The cuticle is smooth. The lateral and inner walls are thin and the former are wavy.

The stomata occur on both the surfaces and the guard-cells are accompanied by subsidiary cells. The guard-cells are elevated and the front cavity is placed in a depression formed by the papillose outer epidermal walls. The stomata on the axis are greatly depressed, as the guard-cells are situated below the surrounding cells (fig. 43). In addition to the subsidiary cells, there are sometimes found one or more cells clasping the guard-cells on one or both sides of the stomata on the axis (fig. 43).

The mesophyll is isobilateral and is composed of palisade tissue. Internal secretory organs are represented by secretory cells with tanniniferous contents in the leaf and axis. In the leaf they are poly- gonal and lie in the lower half of the mesophyll. In the axis there is a sub-epiderma) secretory tissue of one or two layers of tabular cells. Besides, there are numerous outer sclerenchymatous fibres and numerous pith cells with tanniniferous contents. Some of the cells of the medullary-ray-like strands also hold tanniniferous contents. The secretory cells with tanniniferous contents seem to be a charac- teristic feature of the species.

Oxalate of lime is abundantly found in the form of large cluster? ed crystals near the veins in the leaf. In the axis cells with clustered crystals occur in the outer sclerenchymatous fibres, in the cells of tie medullary-ray-like strands and in the pith.

The abundance of tanniniferous substance and of oxalate of lime in the leaf and axis gives an acrid taste to the tissues of the plant and makes it inedible by animals. Abundance of tannin also protects the tissue of the plant from desiccation. The veins are enclosed in green bundle-sheaths. Larger veins occur as usual in the middle of the mesophyll. Besides these, there are smaller veins near the lower epidermis. The vein of the mid-rib is protected above and below by strands of sclerenchyma and is vertically transcurrent below by colourless parenchyma.

The leaf and axis are devoid of clothing and glandular hairs.

Structure of the Axis : — The epidermis consists of small tabular cells with outer and inner walls very greatly thickened. Outer walls are convexly arched outwards. Lateral walls are straight. The cuticle is thick and smooth.

The cortex is characterised by a sub-epidermal tissue of tabular cells with tanniniferous contents. The assimilatory tissue which lies below the secretory tissue is composed of chlorophyll containing parenchyma.

The pericycle is composed of large groups of stone cells situated on the radii of the vascular bundles. Besides these pericyclic groups of stone cells, there is a tissue of sclerenchymatous fibres with larger lumina, continuous with the medullary-ray-like structures between the vascular bundles. There are a few scattered stone cells with walls much thickened and radially striated and with small lumina, on the outer margin of the sclerenchymatous tissue and in the soft bash

The wood is composed of large xylem bundles separated by broad strands of radially elongated thick-walled cells resembling medullary-ray cells. These seem to be continuous with the scleren- chymatous tissue outside the pericyclic groups of stone cells. )

There are isolated cases of sclerotic cells with canals, as large in size as the vessels and situated on the upper side of the xylem near the medullary-ray-like strands. Interfascicular wood-pro- senchyma is not developed. Wood-parenchyma occurs in groups at the inner margin of the xylem bundles.

The pith is composed of thick-walled cells.

PORTULACEAE.

Portulaca oleracea L. (Leaf only).— Clustered crystals in the leaf small and numerous.

Portulaca quadrifida L. (Leaf and Axis). Clustered crystals in the mesophyll large and few.

Structure of the Leaf : — The epidermis is composed of polygonal cells with outer and inner walls thickened. The outer walls are arched convexly outwards and are granulated. Stomata are more numerous on the lower surface. The guard-cells are elevated and accompanied by subsidiary cells. The front cavity is on a level with the surface. The mesophyll is composed almost wholly of aqueous tissue, the vascular bundles of the veins being surrounded' by palisade parenchyma. Internal secretory organs occur neither in the leaf -nor in the axis.

Oxalate of lime occurs in the form of clustered crystals in the aqueous cells of the mesophyll and in the cortex and pith of the axis.

The veins are embedded and are not provided with bundle sheaths ; they are surrounded by palisade parenchyma.

The leaf and axis are devoid of hairs.

Structure of the Axis : — The epidermal cells are polygonal with outer and inner walls greatly thickened. The outer walls are con- vexly arched outwards and are granulated. The stipular rings of sil- very long hairs reflect light and protect the axis and leaves against intense light and heat.

The cortex is formed on its outer side of an extensive tissue of thin- walled parenchymatous cells filled with starch granules and on its inner side of chlorophyll containing parenchyma. The cells of the outermost layer of the cortex are collenchymatous. The cortex may occasionally form an aqueous tissue.

The sclerenchymatous pericycle is not developed.

The vascular system is composed of deeply placed vascular bun- dles separated by thin-walled uniseriate medullary rays. Vessels are small and are arranged in complete rows. The vascular ring is sur- rounded by green parenchyma. The nearness of the assimilatory tissue to the vascular bundles brings about a quick distribution of the products of assimilation.

(To be continued)

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