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

THE

Journal of Indian Botany.

Vol. I. OCTOBER, 1919. No. 2.

THE PHYSIOLOGICAL ANATOMY OF THE

PLANTS OF THE INDIAN DESERT


BY

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

St. Xavier's College, Bombay.


PREFACE.

I had the opportunity of visiting a portion of the great Indian Desert, in the company of Fr. Blatter and Prof. Hallberg, in the months of October and November 1917. The year was remarkable for its abnormal rainfall of over 40 inches as against the average of 10 — 13 inches ; and the herbaceous flora had survived till the time of our visit. On seeing the plants from the different habitats of the Desert identified by Fr. Blatter and Prof. Hallberg, it occurred to me that a treatise on the physiological anatomy of the Indian Desert plants would not be out of place. For while much has been written on other desert floras, nothing has been done in that line of any Indian desert flora.

I set to work, with the view to carrying out my idea and the following treatise, in which I have confined myself to that portion of the Indian Desert which is marked in the map, is the result of my investigations.

I have taken considerable care to provide accurate sketches of the transverse sections of the leaves and the axes, as it is generally found that accurate figures give a clearer idea than long explanatory notes. The drawings have been made with the aid of Abbe's Camera Lucida ; and the different powers of the oculars and objectives have been noted. I have used a Zeiss's microscope and generally Zeiss's apochromatic objectives and compensating oculars.

I hope the essay will prove an addition to our knowledge of the Desert Flora in particular and of the comparative anatomy and physiology of plants in general.

I must use this opportunity to thank Mr. M. V. Unakar, Acting Director of the Bombay and Alibag Observatories for the

meteorological data of the Indian Desert.

INTRODUCTION.

To one who has the opportunity of visiting the Desert, the flora will at once appear striking and in many respects different from that inhabiting other more favoured provinces. The general barrenness of the country, the dry practically rainless climate and the scorching heat of the sun, not to omit the general usceptibility to the wind, have so modified the external organs of the desert plants, that it is but natural to conclude that the internal structure and the processes that are going on in the plants must in like way have been acted upon by these external factors.

Physical Aspects of the Indian Desert.

Some information about the topography, geology and the meteorological data of the area under consideration will elucidate the remark.

(a) Topography. — The portion of the Great Indian Desert, under consideration, is included in the two states Jodhpur and Jaisalmer and forms a square having the four towns Jodhpur, Bap, Jaisalmer and Balmer at its four angles. The general aspect is that of a succession of dry undulating plains and rolling sand-dunes of all sizes and shapes varying from 2 to 3 miles in length and 20 to 400 ft. in height. It is sparingly dotted with low bushes and isolated tufts of curious- looking plants, relieved here and there by green succulents and candelabra-like Euphorbias. Shifting sands are common and continually changing in size and shape. Villages are few and far between and consist of a few huts located round a well or a tank.

{b) Geology. — The region under survey is covered for the most part with wind-blown sand-dunes which are of the transverse type, i.e., have their longer axes at right angles to the direction of the prevailing winds. From beneath these, rocks of earlier age crop out as isolated hills. Near Jodhpur the oldest rocks are schists belonging to the Aravalli system. These are overlain by rocks of volcanic origin, the Mallani series, with conglomerate at the base. Upon these, rest sand-stones of the Vindhyan age. At Balmer the rocks consist of sand-stones, grits and conglomerates containing ill-defined fossil remains. At Jaisalmer sand-stones and lime-stones of Jurassic age occur and Nummulitic rocks are common.

(c) Meteorological data. — It should be noted that the year 1917, the year of the tour, was remarkable on account of the abnormal amount of rainfall. The data of the normal maximum and minimum temperature, relative humidity of the air, rain-fall and number of rainy days are obtained by averaging the observations of 14 years (pp. 3fi & 37).

(d) General plan. — As regards the general plan and arrangement

of the subject the orders have been described in the sequence of Bentham and Hooker's system of classification. I have chosen the

representative plants from the different parts of the desert and have examined fifty orders, 125 genera and 165 species. In dealing with the individual order, I have described the specific characters, the structure of the leaf and the structure of the axis and when necessary I have appended a general review of the order. I have omitted the structure of the root, as generally it is not available in herbarium specimens. The specific characters that are considered, are just those that will be useful in the diagnosis of the species. The different structures are considered in detail under the heads of "The structure of the leaf" and "The structure of the axis". The characters which are common to both the leaf and axis are usually dealt with jointly under the structure of the leaf as they are more prominent in the leaf.

I have embodied the interpretations of the various modifications of the different tissues in the descriptions of the structures of the leaf and the axis, and in the general review of the order, so that the descriptions can be said to contain at once an account of the anatomy and physiology of the plants in question. The concluding remarks at the end of the principal part of the work serve as a concise and complete summary of the treatise.

{e) Method. — As regards the method employed in preparing the herbarium material for the section work, small pieces of the leaves and the axes were soaked in water for about two hours and then hardened in formalin alcohol for about a day. The sections which were cut in 90% alcohol were placed, before mounting in glycerine, in a few drops of lactic acid on a slide and slightly warmed over a burner, so that the cells of the different tissues might expand to their proper dimensions.

(f) A suggestion. — The idea of employing micro-anatomical and micro-chemical characters for systematic purposes originated in times as early as those of Linnceus, and has been repeatedly put forward by several botanists, Radlakofer being considered as the founder of the anatomical method. It would be presumptuous on my part to discuss the merits of the method for systematic purposes; but from what little I have observed in my study of the physiolo- gical anatomy ol the desert flora, I have grounds for believing that the study of Systematic Botany would considerably progress were more attention paid to anatomical characters than has heretofore been done. The method is no doubt laborious and a systematic botanist would be loth to adopt it, owing to the huge amount of the material submitted to him for identification from all sides. I admit this difficulty and suggest that the anatomical characters should be used at least as confirmatory evidence in establishing genera and species.

MENISPERMACEAE.

Cocculus cebatha DC. —Figs. 1, 2. (p. 39)— Epidermis of the leaf composed of thin-walled tabular cells. Stomatu occurring on both the surfaces. Subsidiary cells accompanying the guard-cells. Mesophyll composed wholly of palisade cells. Internal glands absent. Pith cells containing clusters of acicular crystals of oxalate of lime. Clothing hairs bicellular and curved. Glandular hairs absent. Veins embedded and enclosed in green sheaths. Axis slightly ribbed, ribs strengthened by a few sclerenchymatous fibres. Epidermal cells of the axis tabular with outer walls greatly thickened and cuticularised. Cortex formed of chlorophyll containing parenchyma. Pericycle composed of large groups of stone-cells. Wood formed of xylem bundles separated by broad medullary rays extending to the cortical chlorenchyma. Groups of cells resembling bast fibres on the inner face of the xylem bundles. Pith composed of thick-walled cells.

Structure of the leaf

Epidermis is composed of tabular cells, with outer walls flat and a little thickened. Lateral and inner walls are thin and the former are straight. Stomata are accompanied by subsidiary cells and are more numerous on the under-surface. Guard-cells are situated on a level with the surrounding cells, with the front cavity slightly depressed, or on a level with the surface, fig 1. The mesophyll is composed of a homogeneous tissue of short palisade cells. Internal glands are absent in the leaf as well as in the stem. Oxalate of lime is not found in any form in the leaf. Veins are embedded and are enclosed in green bundle sheaths.

Veins of the mid-rib, which is prominent above and below, are verti- cally transcurrant above and below by collenchyma; the bundles are protected on the lower side by small groups of stone-cells.

Hairy covering on the leaf and axis consists of clothing hairs. Clothing hairs are made up of a short thin-walled basal cell and of a long curved thin- walled pointed terminal cell.

Structure of the axis

Epidermal cells are small and tabular with outer walls very greatly thickened and cuticularised. Lateral and inner walls are thin and the former are straight. The axis is slightly ribbed, the ribs being strengthened by a few sclerenchymatous fibres.

The cortex is formed of chlorophyll containing parenchyma which extends to the medullary rays between the groups of stone-cells of the sclerenchymatous pericycle. The pericycle consist of large groups of stone-cells separated by the chlorophyll containing parenchyma of the cortex. The wood (fig. 2) is composed of large xylem bundles separat- ed by broad medullary rays which come into contact with the chloro- phyll containing parenchyma of the cortex. Vessels are large and have simple perforations. Groups of cells, resembling bast fibres, are present on the inner side of the xylem. Inter fascicular wood-prosen- chyma is not developed. The endodermis is not differentiated. The soft bast occurs in groups on the outer side of the xylem, separated by medullary rays. The pith is composed of thick-walled cells and some of these contain small clusters of acicular crystals of oxalate of lime.

Woody. — The middle tissue of the mesophyll composed of large colourless polygonal cells with water-storage function. Neither sur- face of the leaf grooved. Axis not furrowed. Assimilatory tissue of the axis composed of short palisade cells. Sclerenchymatous pericycle in the form of a few scattered bast fibres. Vascular ring broad with vessels uniformly distributed in incomplete rows and more numerous in the lower half.

Farsetia macrantha Blatt and Hall, Flos. 4, 7, 8.Herbaceous.— Middle tissue of the mesophyll composed of chlorophyll containing horizontally elongated cells with assimilatory function. Lower sur- face of the leaf characterised by ridges and furrows. Axis furrowed. Assimilatory tissue of the axis formed of an outer portion of palisade cells and of an inner portion of chlorenchyma. Sclerenchymatous pericycle in the form of closely placed large groups of bast fibres. Vascular ring undulate and composed of small vascular bundles connected by narrow strands of interfascicular wood prosenchyma with cells resembling stone cells.

Structure of the Leaf.

Epidermis consists of horizontally tabular cells with outer walls greatly thickened and arched convexly outwards. Lateral walls are undulate. Stomata occur on both the surfaces and are accompanied by subsidiary cells one of which is smaller than the other two. The front cavity is placed in a depression formed by outer thickened walls of the epidermal cells. Guard cells are placed in the plane of the surrounding cells. (Fig. 5.) Stomata on the axis are numerous and have the same characters as those on the leaf. Mesophyll is

isobilateral, and is characterised by a middle tissue which is composed of large thin-walled colourless polygonal cells, perhaps acting as water reservoirs in F. jacquemontii (Fig. 3) and of horizontally elongated green cells in F. macrantha (Fig. 7.) Internal secretary organs

To he inserted in the Journal of Indian Botany Vol. I No. 2 to face page 40.

The following to be inserted after first paragraph, page 40.

CRUC1FERAE.

Farsetia jacqucmontii Hook., Figs. 3, 4, 5, 6. 781-6 sclerenchymatous pericycle. The pericycle consist of large groups of stone-cells separated by the chlorophyll containing parenchyma of the cortex. The wood (fig. 2) is composed of large xylem bundles separat- ed by broad medullary rays which come into contact with the chloro- phyll containing parenchyma of the cortex. Vessels are large and have simple perforations. Groups of cells, resembling bast fibres, are present on the inner side of the xylem. Inter fascicular wood-prosen- chyma is not developed. The endodermis is not differentiated. The soft bast occurs in groups on the outer side of the xylem, separated by medullary rays. The pith is composed of thick-walled cells and some of these contain small clusters of acicular crystals of oxalate


Epidermis consists of horizontally tabular cells with outer walls greatly thickened and arched convexly outwards. Lateral walls are undulate. Stomata occur on both the surfaces and are accompanied by subsidiary cells one of which is smaller than the other two. The front cavity is placed in a depression formed by outer thickened walls of the epidermal cells. Guard cells are placed in the plane of the surrounding cells. (Fig. 5.) Stomata on the axis are numerous and have the same characters as those on the leaf. Mesophyll is isobilateral, and is characterised by a middle tissue which is composed of large thin-walled colourless polygonal cells, perhaps acting as water reservoirs in F. jacquemontii (Fig. 3) and of horizontally elong- ated green cells in F. macrantha (Fig. 7.) Internal secretary organs are not found in either of the species. Veins are embedded and are

provided with sheaths of thickened green cells. The bundles are accompanied by arcs of collenchyma on the lower side, protecting the phloem of the veins. Hairy covering on the leaf and axis con- sists of densely placed clothing hairs. The hairs are unicellular, two- armed with their thin walls bearing knobs incurstated w :i "h carbonate of lime, fig. 4. The hairs are appressed, filled with air and white ; and protect the plants from insolation by reflecting the rays of light. Glandular hairs do not occur in either of the species.

Structure of the axis.

Epidermis is composed mostly of vertically tabular cells with outer and inner walls greatly thickened and-cuticluarised, much more so in F. macrantha. Lateral walls are thin and undulate.

Primary cortex is characterised by assimilatory tissue composed of short palisade cells in F. jacquemontii (fig. 6) and of palisade tissue on the outer side and chlorencyma on the inner side in F. macrantha (fig. 8). Sclerencymatous pericycle is represented in F. jacquemontii (fig. 6) by a few scattered bast fibres, and in F. macrantha by numer- ous closely placed groups of bast fibres, (fig. 8.) The wood in F. jacquemontii (fig. 6) is quite composite and has vessels uniformly distributed in incomplete rows, the vessels being more numerous and larger in the lower half. In F. macrantha (fig. 8) the vascular ring is undulate and is composed of very small xylem bundles connected by narrow strands of interfascicular wood prosenchyma formed of thick walled cells having small lumina. There are large groups of wood parenchyma enclosing the lower portions of the xylem bundles. Medullary rays do not occur in either of the species.

The pith is composed of thin-walled cells.

Capparidaceae.

Cleome papillosa Steud. Figs. 10, 11, 12, 17, 18. Herbaceous. Epidermal cells with outer walls strongly papillose. Guard cells in the plane of the surrounding cells. Mesopbyll composed of palisade tissue on the adaxial side and of arm-palisade tissue on the abaxial side. Veins not provided with bundle sheaths. Internal glands absent. Glandular hairs multicellular and capitate. Outer walls of the epidermal cells of the axis superficially granulated. Assimilatory tissue in the axis formed of chlorophyll containing parenchyma. Pericycle consisting of long, thin groups of stone cells. Wood composite. Soft bast occuring in groups. Pith formed of thick- walled cells.

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(To be continued.)

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