The Journal of Indian Botany/Volume 2/October 1921/The Physiological Anatomy of the Plants of the Indian Desert
THE
Journal of Indian Botanp,
Vol. II. OCTOBER, 1921. No. 10.
THE PHYSIOLOGICAL ANATOMY OF THE PLANTS OF THE INDIAN DESERT
BY
T. S. SABNIS, B.A., M.SC,
St. Xavier's College, Bombay.
{Continued from p. 227).
GRAMINEAE—(Contd.)
Pappophorura elegans Nees.--Figs. 351, 352. Grooves deeper on the lower surface. Margins pointed and with small stereome bundles. Hairs spiny, long and unicellular. Numerous long unicellular hairs on the axis. Stomata more numerous on the lower surface. Palisade cells forming arcs on sides of veins. Veins vertically trans-current and provided with complete bundle sheaths. Articulation tissue on the upper side of mesophyll, and extensive. Mechanical tissue in the leaf forming I-girders. Assimilatory tissue in the axis and palisade cells along smaller vascular bundles and chlorenchymatous between them. A continuous layer of sheath-cells on the inner side of the assimilatory tissue, Mechanical tissue in the axis in the form of a stereome tube supplemented by isolated sub-epidermal girders and I-girders. Webs formed by mixed small vascular bundles. Larger vascular bundles few and mostly apposed to the inner side of stereome tube. Medullary tissue of thin-walled cells.
Eragrostis interrupta Beam. — Figs. 353, 354, 355. Grooves on either surface not deep. Margins pointed and with small stereome bundles. Hairs spiny. Stomata more numerous on the upper surface. Articulation tissue in the upper half of the mesophyll. Palisade cells forming arcs on sides of veins. Veins vertically transcurrent. Smaller veins apposed to lower epidermis. Bundle-sheaths complete round smaller veins and in the form of arcs on sides of larger veins. Mechanical tissue in the leaf in the form of I-girders alternating with isolated sub-epiderinal girders on the upper side. Assimilatory tissue of arcs of palisade cells on the outer side of smaller vascular bundles and chlorenchyrnatous between them. Mechanical tissue farming a stereome tube supplemented by isolated sub-epidermal girders and I-girders. Webs formed by strips of stereome bundles. Smaller vascular bundles with arcs of palisade cells and of sheath- cells on the leptome side and with the hadrome portion embedded in stereome tube. Larger bundles numerous in the medullary tissue. Medullary tissue formed of thin-walled cells.
Eragrostis pilosa Beauv. — Fig. 356. Grooves not deep, Margins pointed and with small stereome bundles. Hairs spiny and more numerous on the lower surface. Stomata only on the lower side. Articulation tissue confined to the plane of epidermis and formed of long horizontal strands. Palisade tissue forming arcs on sides of veins. Veins vertically transcurrent. Bundle-sheaths complete round smaller veins. Mechanical tissue in the leaf forming I-girders and in the axis forming stereome tube supplemented by isolated sub-epidermal girders. Assimilatory tissue in the axis chlorenchyrnatous. Smaller vascular bundles embedded in stereome tube. Larger bundles in the medullary tissue, few and enclosed in rings of stereome. Medullary tissue of thick-walled cells towards the periphery and of thin-walled cells towards the centre.
Desmostachya bispinata Stapf.— (Eragrostis cynosu- roides Beauv.) — Figs. 357, 358. Grooves not deep. Hair3 spiny. Stomata more numerous on the upper surface. Articulation tissue extending between two surfaces. Palisade tissue forming arcs on sides of veins. Veins with arcs of complete girders of sheath-cells. Veins vertically transcurrent. Mechanical tissue in the leaf forming I-girders and in the axis forming isolated sub-epidermal girders alter- nating with I-girders. Assimilatory tissue chlorenchyrnatous. Larger vascular bundles with arcs of stereome on the outer side. Medullary tissue of thin-walled cells.
Oropetium Thomaeum Trin — Fig. 359.— Grooves deep and alternating on two surfaces. Margins pointed and with small stereo- me bundles. Clothing hairs unicellular. Club-shaped glandular hairs on the upper surface. Stomata more numerous on lower sur- face. Articulation tissue in the upper half of mesophyll and not extensive. Bundle-sheaths horse-shoe shaped and incomplete on the lower side. Palisade tissue forming arcs on sides of veins. Veins apposed to lower epidermis and vertically transcurrent above by stereome bundles. Mechanical tissue in the leaf forming isolated sub- epidermal girders on the upper side above the veins. Structure of the Leaf. — The epidermal cells differ much in size and shape in different species as well as on two surfaces in the same species. They are either polygonal as in the greater number of species ; or vertically elongated either on both the surfaces as in G. catharticus, E. flagellifera and species of Andropogon or only on the upper surface as in D. sanguinalis, E. Royleamis and E. aristata. They are extremely small in D. bispinata and in species of Aristida. The cells near the stereome bundles are very small. The outer walls are thickened and silicified. The lateral walls are thin and straight. The former are papillose in E. aristata (fig. 349), G. villosa and 0. Tho- maeum, the papilloso differentiation being quite conspicuous on the upper surface in the former. The upper epidermis is usually char- acterised by furrows of various depths and the epidermal cells of the furrows are quite characteristic. They are vertically elongated, thin- walled, colourless and narrowed above, and they form the articulation tissue. The articulation tissue either occupies the upper half of the mesophyll, or it extends in the form of vertical strands almost to the lower surface, the lower half of the strand being formed of horizontally elongated thin-walled cells as in C. villosa (fig. 345), P. elegans (fig. 351) species of Eleusine (figs. 346, 349), E. Royleanus (fig. 323), L. Senegal- ensis (fig. 325), and D. bispinata (fig. 357j. In E. Royleanus (fig. 326) epidermal cells on the lower surface are characterised by distinct angular thickenings of the outer walls. The cuticle is toothed between the cells in species of Aristida.
The margins are curved upwards and are strengthened by stereome bundles. The margins are sharp or bluntly pointed in T. S. of the leaf-blade. The stereome bundles are larger in the latter.
Guard-cells are accompanied by subsidiary cells ; they are either in the plane of the surrounding cells or elevated above that plane (figs. 347, 354). The front cavity is placed in a depression formed by outer thickened epidermal wall, the depression being very great in case of papillose outer walls of E. aristata (fig. 349). The stomata either occur only on the upper surface as in E. hirsutus or only on the lower as in E. pilosa, or more numerous on the upper surface as in A. funiculata, P. turgidum, D. bispinata, E. interrupta and L. senegalensis, or more numerous on the lower as in other members.
The palisade tissue forms arcs on sides of vertically transcurrenfc veins and complete girders round non-transcurrent veins. Complete girders of palisade cells are found round all the veins, whether they are vertically transcurrent or not in D. sanguinalis and P. turgidum. The palisade cells of the adjacent veins are in contact when the strands of the articulation tissue extending between the two surfaces do not alternate with the veins. Sometimes adjacent palisade arcs or girders are connected together by transverse strands of palisade cells. In E. hirsutus there is an extensive tissue of thin-walled parenchymatous cells towards the upper surface on either side of the mid-rib ; this tissue seems to form an articulation tissue which adds to the strength of the system of strands of the articulation tissue below the furrows.
Spongy tissue is not developed in any of the members and thus the ventilating system is quite reduced. The articulation tissue forms a characteristic feature of species of Gramineae ; it is composed of thin-walled cells with a double function — that of collecting water and that of assisting the halves of the leaf-blade to curve upwards. The conical shape of the cells of the upper portion of the strands of the articulation tissue is especially suited to this purpose.
The veins are provided with bundle-sheaths of thick-walled green cubical cells. The bundle-sheaths form complete rings round non-transcurrent veins and arcs on the sides of vertically transcur- rent veins excepting E. aristata in which all the vertically transcurrent veins are provided with complete sheaths. The bundle-sheaths in 0. Thomaeum and L. senegalensis are horse-shoe shaped and are incom- plete on the lower side. As regards the function of bundle-sheaths, they many form the means of inter-communication between the vessel and the assimilatory tissue, as well as assist the latter in photosynthesis. The veins are embedded in D. sanguinalis and in species of Panicum, while they are vertically transcurrent above and below by stereome bundles in D. bispinata, C. villosa, G. Boyleana. The veins are appo- sed to the upper epidermis and are vertically transcurrent below by stereome bundles in 0. Thomaeum. In E. interrupta the larger veins are vertically transcurrent above and below by stereome bundles ; and the smaller veins are apposed to the upper epidermis and are vertically transcurrent below by stereome bundles. In other members the lar- ger veins are vertically transcurrent above and below by stereome bundles except in E. Boyleanus, C. catharticus and E. flagellifera, where aqueous cells are found between the vascular bundles and stereome bundles on one side or both sides ; the smaller bundles are embedded.
The veins either all lie in the same plane where the furrows on both the surfaces are more or less equally deep, or they are placed in two distinct planes where the furrows on the upper surface are deeper than on the lower — the veins below the furrows being situated in the lower plane. This arrangement of veins is well adapted to the curving habit of the leaf-blade. The mechanical tissue is composed of stereome bundles on the lower side of all veins, except in cases where the veins are apposed to the lower epidermis, and of those on the upper side of vertically trans- current and embedded veins. In the case of embedded veins the stereome bundles form I-girders the webs of which are formed by vascular bundles either unmixed as usually in vertically transcurrent veins, or mixed. The margins especially when they are bluntly pointed are strengthened by large stereome bundles.
The stereome bundles in A. funiculata are large and numerous and sometimes form a more or less continuous layer on the lower surface of the leaf- blade (fig. 335). The abundance of strengthening tissue on the lower surface is necessary to protect the leaf-blade against the tension produced by the curving upwards of the leaf-halves.
The stereome bundles on the upper side, supplemented by the articulation tissue, form an adequate strengthening tissue against strains of compression. The abundance of the articulation tissue assists the leaf-halves to regain their normal position, The occurrence of strengthening tissue on the upper surface, as extensive as on the lower, prevents the articulation tissue from performing its function.
The hairy covering on the leaf consists usually of short spiny unicellular clothing hairs with somewhat dilated bases. They are more numerous on the upper surface, usually arising from epidermal cells over the veins and arching over the furrows. Besides spiny hairs, there are long unicellular hairs arising from articulation cells of the epidermis on both sides in P. elegans (fig. 351) and E.flagelli- /era (fig. 346). In E. Boyleanus there occur only long unicellular hairs which arise from articulation cells on the upper surface. Spiny hairs are replaced by short bluntly pointed unicellular hairs in E. aristata and in species of Andropogon. The hairy covering is not found on the axis except in a few cases. In P. elegans and E. hirsutus (fig. 330) there are numerous long unicellular hairs. Short spiny unicellular hairs arise from epidermal cells over stereome bundle in E. flag ellij "era and G. Eoyleana. The absence of a hairy covering on the axis can be accounted for by the highly thickened and silicified outer epidermal walls.
The abundance of spiny hairs is the outcome of a deficient supply of water ; and their usual position above the veins is due to localised extra nourishment. The dilated bases of the spiny hairs are capable of imbibing moisture and so the hair covering has a double function, that of imbibing moisture and that of protecting the surface against strong glare and light which accelerate transpiration. Glandular hairs are of rare occurrence. They occur on the upper surface of the leaf-blade of 0. Thomaeum, on the axis of G. Boleana (fig. 342) and on the leaf-blade and axis of D. bispinata. They are composed of a stalk-cell and of a club-shaped head which is divided by horizontal walls.
Structure of the axis. — The epidermal cells are small and have the outer walls greatly thickened and silicified. The stomata are accompanied by subsidiary cells. The guard-cells are elevated and the front cavity is placed in a depression formed by outer thickened epidermal walls.
The cortex is characterised by an extensive sclerenchymatous tissue with groups of the assimilatory tissue embedded in it. The assimilatory tissue, in A. hirtigluma, P. turgidnm, E. interruputa, E. aristata, and G. Royleana is composed of groups of palisade cells which are separated from the stereome by single layers of thick- walled cubical cells containing chlorophyll and resembling bundle- sheath cells.
The palisade cells form a continuous ring in P. elegans and E. hirsutus. An assimilatory tissue is not found in D. sanguinalis, E. Boyleanus, L. senegalensis and species of A ndropogon. In other members the assimilatory tissue is chlorenchymatous and is not accompanied by a sheath-like layer.
The mechanical tissue in the axis is represented by a stereome tube supplemented by isolated sub-epidermal girders of variable sizes except in P. elegans and E. hirsutus. Flanges are given out from the outer side of the stereome tube at more or less regular intervals and in some cases (figs. 340, 355), they unite with supplementary sub-epidermal girders, thus bringing the two systems into contact and contributing additional strength to the whole mechanical system. In species of Aristida (figs. 336, 337), Panicum (figs. 320, 322) and of Eleusine (fig3. 348, 350), in P. elegans (fig. 352), G. Boyleanus (fig. 343) and C. catharticus (fig. 324) the smaller vascular bundles are embedded in the stereome strands, formed by sub-epidermal girders and by flanges of the stereome tube.
The embedded small vascular bundles are mixed with the accom- panying sheaths (fig. 320) only, or with both sheaths and girders of the assimilatory tissue (figs. 340, 343, 352). In other cases where the vascular bundles are embedded they are unmixed. This sort of arrangement of the mechanical tissue is quite effective, as it forms an adequate strengthening tissue without preventing the assimilatory tissue from performing its function.
In D. sanguinalis, E. Boyleanus, L. senegalensis and in species of Andropogon there is a composite sub-epidermal stereome tube in which unmixed small vascular bundles are embedded. In D. bispinata there is no stereome tube and the mechanical tissue is represented by isolated sub-epidermal girders alternating with sub-epidermal I-girders.
Besides the two systems of the mechanical tissue described above, the vascular bundles in the medullary tissue are supported by arcs of stereome on the outer side in D. bispinata and in species of Eleusine, or are enclosed in rings of stereome in E. pilosa, C. villosa, E. hirsidus, L senegalensis, C. catharticus and species of Aristida. The sclerenchyma in these cases chiefly protects the vascular bundles and is therefore of a local value ; it does not add much to the strength of the mechanical tissue system.
The vascular system consists of vascular bundles of two sizes. The smaller bundles are embedded in the stereome tube, when it is developed, except in E. kirsutus (fig. 330j in which they are embedded in the assimilatory tissue. Of the larger vascular bundles, the peri- pheral ones are mostly apposed to the inner side of the stereome tube a few being embedded in it ; and the rest are placed in the medullary, tissue in which they are supported by arcs or rings of stereome in some cases as already described.
The larger vascular bundles in G. Royleana (fig. 343) are more or less arranged in a ring and are embedded in the stereome tube. The vascular bundles of the larger type in E. kirsutus are numerous and traverse the whole of the medullary tissue.
The medullary tissue consists of thin-walled cells except in E. hirsutus and L. senegalensis where it consists throughout of thick- walled cells filled with granular contents. Medullary cells of G. Roy- leana are also filled with starch grains.
General Review. — The margins of leaf-blades are curved upwards. The articulation tissue is well developed ; it is of epidermal origin and has a double function, that of an aqueous tissue and that of bringing about the curving movements of the leaf-halves. Leaf-blades are more or less furrowed on both the surfaces. The hairy covering is denser on the upper surface and usually consists of short, unicellu- lar spiny hairs arising from epidermal cells above the veins and arching over the furrows. In some members there are long unicellu- lar hairs, arising usually in the case of leaves, from articulation tissue cells. The external glands occur in 0. Tliomaeum, G. Royleana and D. bispinata ; and are composed of a stalk cell and of a club shaped head. The sfcomata are depressed and are either present only on the upper surface or are more numerous on the upper surface. The guard-cells are elevated arid are accompanied by subsidiary cells one on either side. The veins are numerous and are enclosed in complete or incomplete sheaths. The larger veins are vertically transcurrent above and below by stereome bundles. The assimilatory tissue in the leaf consists of complete girders of palisade cells round the smaller veins and of arcs of palisade cells on sides of the vertically trans- current veins. The spongy tissue is altogether absent. The veins with the accompanying assimilatory tissue are sometimes separated from one another by vertical strands of articulation tissue.
The mechanical tissue in the leaf-blade occurs in the form of I-girders the webs of which are formed by mixed or unmixed vascular bundles of the veins. The margins especially when thay are bluntly pointed are strengthened by large stereome bundles. The epidermis of the axis consists of small cells with the outer walls greatly thick- ened and silicified. The assimilatory tissue consists of palisade tissue or of chlorenchyma ; it is absent in some members. The mechanical tissue is represented by a stereome tube supplemented by isolated sub-epidermal girders.
Vascular bundles are of two sizes, the smaller ones being usually embedded in stereome strands formed by the sub-epidermal girders and by flanges of the stereome tube. Of the larger vascular bundles the peripheral ones are usually apposed to the inner side of the stereome tube and the rest are scattered in the medullary tissue. The medullary tissue usually consists of thin-walled cells, which, in some members, are filled with starch grains.
FILICINAE
Actiniopteris dichotoma Bedd. — Figs. 360, 361. A segment of the frond : — Upper epidermis of sclerotic cells and accompanied by sub-epidermal stone tissue. Lower epidermis of small tabular cells with outer walls thickened and toothed, and with groups of stone- cells intercalated amongst them below the stele- Stomata on the lower surface and accompanied by ordinary epidermal cells. Assimila- tory tissue consisting of chlorenchyma. Stele supported above and below by epidermal stone-tissue. Hairs absent.
Stipe : — Epidermal cells sclerosed except at the angular por- tion, and accompanied by sub-epidermal stone-tissue. Cuticle tooth- ed. Stomata in angular portion. Assimilatory tissue consisting of chlorenchyma. Hairs long and unicellular. Stele in the centre. Structure of the Segment. — The epidermis of the frond-segment on the upper surface (fig. 360) consists of sclerotic cells with outer walls toothed in the middle. The sclerotic epidermis is accompanied by a sub -epidermal tissue of stone-cells which have the same size and structure as those of epidermal sclerotic cells. The sub-epidermal stone-tissue stops short a little behind the margin which is curved downwards over the sporangia forming a kind of an indusium. The margin presents a filamentous structure in T. S. and is strengthened by a spiral thickening of the wall. The lower epidermis is formed of tabular cells with the outer walls thickened and cuticularised ; there are groups of stone-cells intercalated amongst epidermal cells above the stele. The cuticle of lower epidermal cells is also toothed in the middle of the cells.
Structure of the Stipe. — The epidermal cells of the stipe (fig. 361) are sclerosed, except at the angular portions on the upper side. The sclerosed epidermis is further strengthened by a sub-epidermal tissue of stone-cells. The epidermis at the angular portions is formed of chlorenchymatous cells with outer walls thickened. The outer walls of the sclerosed epidermal cells are toothed in the middle of the cell. The abundant development of epidermal and sub-epidermal scleren- chyma has chiefly the function of reducing transpiration which is very vigorous in Ferns ; and it is a result of the deficiency of water.
Stomata occur on the lower surface of the segment and in the angular portion of the stipe, and are accompanied by ordinary epidermal cells. The guard-cells are much elevated and the front cavity is situated above the surface.
Hairy covering is absent on the segment. On the stipe there occur long unicellular thick-walled hairs strengthened in the basal portion by the spirally thickened wall (fig. 261). The external glands are not found on the segment or on the stipe.
The assimilatory tissue in the segment as well as in the stipe is formed of chlorenchyma. In the stipe there are circular spaces in T. S. one near each margin.
The stele in the marginal portion from where the sporangia origi- nate is larger than those in other portions of the pinnule. Steles, except those at the margin, are strengthened on the lower side by groups of stone-cells intercalated amongst epidermal cells (fig. 360). In the stipe there is a single larger stele in the centre.
Plate XXXVI.
351-352. Pappophorum elegans.
351. T. S. of the leaf.
Oc. 4 Com. ; Ob. 3 mm. Ap.
352. T. S. of the axis.
Oc. 2 Com. ; Ob. 3 mm. Ap. 353-355. Eragrostis interrupta.
353. T. S. of the leaf.
Oc. 6 Com. ; Ob. 8 mm. Ap.
354. T. S. of the leaf showing stomata.
Oc. 6 Com. ; Ob. 3 mm. Ap.
355. T. S. of the axis.
Oc. 4 Com. ; Ob. 8 mm. Ap. 356. Eragrostis pilosa. T. S. of the leaf. Oc. 2 Com. ; Ob. 3 mm. Ap.
357-358. Desmostachya bispinata.
357. T. S. of the leaf.
Oc. 2 Com. ; Ob. 3 mm. Ap.
358. T. S. of the axis.
Oc. 4 Com. ; Ob. 8 mm. Ap. 359. Oropetium Thomaeum.
T. S. of the leaf.
Oc. 4 Com. ; Ob. 3 mm. Ap. 360-361. Actiniopteris dichotoma,
360. T, S. of the frond.
Oc. 4 Com. ; Ob. 8 mm. Ap.
361. T. S. of the Eachis.
Oc. 2 Com. ; Ob. 8 mm. Ap-
iV-S.— To get the original dimensions multiply by 1'7,
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