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The Journal of Indian Botany/Volume 1/April 1920/The Physiological Anatomy of the Plants of The Indian Desert

THE

Journal of Indian Botany.

Vol. I. APRIL, 1920. No. 8.

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. 107.)


PAPILlONACEAE-(Contd).

Crotalaria Medicaginea Law.— Figs. 102, 103. Epidermal cells tabular. Mesophyll bifacial. Veins embedded and enclosed in bundle-sheaths. Tannin sacs found near the veins. External glands absent. Assimilatory tissue in the axis parenchy-matous. Pericycle formed of stone-cells. Medullary rays uniseriato. Pith formed of thin-walled cells.

Indigofera linifolia Bets, — Epidermal cells tabular. Meso- phyll isobilateral ; Veins embedded and enclosed in bundle-sheaths. Tannin sacs in the middle of fcha mesophyll, in cortex and pith. Clothing hairs in the form of two-armed trichomes. External glands absent. Assimilatory tissue in the axis chlorenchymatous. Pericycle formed of bast fibres. Medullary rays uniseriate. Pith formed of thin walled cells.

Indigofera cordifolia Heync— Figs. 104, 105. Epidermal cells tabular. Mesophyll isobilateral. Veins embedded and enclosed in bundle-sheaths. Tannin sacs in the middle of the mesophyll, in cortex and pith. Clothing hairs in the form of two-armed trichomes. External glands absent. Assimilatory tissue in the axis chlorenchymatous. Pericycle formed of bast fibres. Medullary rays uniseriate. Pith formed of thin-walled cells.

Indigofera paucifolia Del— Figs. 106, 107. Epidermal cells tabular, Mesophyll isobilateral. Veins embedded and enclosed in bundle-sheaths. Tannin sacs in the palisade tissue, in cortex and pith. Clothing hairs in the form of two«armed trichomes. External glands absent. Assimilatory tissue in the axis chlorenchymatous. Poricycle formed of bast fibres. Medullary rays 1-2 seriate. Pith formed of thick-walled cells.

Indigofera argentea Barm.— Epidermal cells tabular. Meso- phyll isobilateral. Veins embedded and enclosed in bundle-sheaths. Tannin sacs in the middle of the mesophyll, in cortex and pith. Clothing hairs in the form of two-armed trichomes. External glands absent. Assimilatory tissue in the axis chlorenchymatous. Pericycle formed of bast fibres. Medullary rays uniseriate. Pith formed of thin-walled cells.

Indigofera anabaptista Steud,— Epidermal cells tabular. Me- sophyll isobilateral. Veins embedded and enclosed in bundle-sheaths. Tannin sacs in the middle of the mesophyll, in cortex and pith. Clothing hairs in the form of two-armed trichomes. External glands abseut. Assimilatory tissue in the axis chlorenchymatous. Pericycle formed of bast fibres. Medullary rays uniseriate. Pith formed of thick-walled cells.

Psoralea odorata Blatt. and Hall.— Figs. 108. Epidermal cells tabular. Mesophyll isobilateral. Veins vertically transcurrent by means of colourless parenchyma and enclosed in bundle-sheaths. Tannin sacs found near the veins and in the soft bast. Intramural glands found in the leaf. Clothing hairs appressed and muriculate. External glands club-shaped. Assimilatory tissue in the axis chloren- chymatous. Pericycle formed of bast fibres. Medullary rays unise- riate. Pith formed of thick-walled cells.

Tephrosia incana Grah. — Epidermal cells tabular. Mesophyll bifacial. Veins vertically transcurrent by sclerenchyma. Veins provided with bundle-sheaths. Clothing hairs in the form of uniseriate trichomes with muriculate walls. Pericycle composed of groups of stone-cells. Tannin sacs in the middle of the mesophyll. External glands absent. Assimilatory tissue in the axis chloren- chymatous. Pericycle formed of stone-cells. Medullary rays uni- seriate. Pith formed of thin-walled cells.

Tephrosia multiflora Blatt. and Hall— -Epidermal cells tabular. Mesophyll bifacial. Veins vertically transcurrent by scleren- chyma and provided with bundle-sheaths. Clothing hairs in the form of uniseriate trichomes with muriculate walls. External glands absent. Pericycle formed of groups of stone-cells. Tannin sacs in the middle of the mesophyll. Assimilatory tissue in the axis chloren- chymatous. Pericycle formed of stone-cells. Medullary rays uni- seriate. Pith formed of thin-walled cells.

Alysicarpus vaginalis DC— Figs. 109, 110, 111. Epider- mal cells tabular with outer walls toothed. Mesophyll bifacial. Veins vertically transcurrent by sclerenchyma and provided with bundle-sheaths. Tannin sacs absent. Clothing hairs hooked. External glands formed of a stalk-cell and of a globose head. Assimilatory tissue in the axis chlorenchyrnatous. Pericycle formed of stone-cells. Medullary rays 1-2 seriate. Pith formed of thin-walled cells.

Phaseolus trilobus Ait.— Fig. 112. Epidermal cells tabular with inner walls gelatinised. Mesophyll bifacial. Veins vertically transcurrent by collenchyma. Bundle-sheaths absent. Tannin sacs in the palisade tissue. Clothing hairs in the form of uniseriate trichomes with muriculate walls. External glands culb-shaped. Assi- milatory tissue in the axis chlorenchmatous. Pericycle formed of bast fibres. Medullary rays 1-2 seriate. Pith formed of thin-walled cells.

Rhynchosia arenaria Blatt. and Hall— Figs. 116, 117. Epi- dermal cells tabular. Mesophyll bifacial. Veins vertically transcurrent by sclerenchyma and provided with bundle-sheaths. Tannin sacs found in the middle of the mesophyll and in soft bast. Clothing hairs in the form of uniseriate trichomes with muriculate walls. External glands consisting of an uniseriate stalk and of a spherial head. Assi- milatory tissue in the axis chlorenchyrnatous. Pericycle formed of stone-cells. Medullary rays 2-3 seriate. Pith formed of thin-walled cells.

Rhyncosia rhombifolia Blatt. and Hall—Figs. 113, 114, 115.

Epidermal cells tabular. Mesophyll bifacial. Veins vertically transcurrent by sclerenchyma and not provided with bundle-sheaths. Tannin sacs found in the middle of the mesophyll and in soft bast. Clothing hairs in the form of uniseriate trichomes with muriculate walls. External glands formed of an uniseriate stalk and of a spheri- cal head. Assimliatory tissue-in*the axis chlorenchyrnatous. Pericycle formed of stone-cells. Medullary-rays 2-3 seriate. Pith formed of thick-walled cells.

Structure of the Leaf: — Epidermal cells may be tabular with straight lateral walls, or may be polygonal with lateral walls undulated, as in species of Crotalaria fig, 100 and Heylandla latebrosa fig. 99. Outer walls are thickened and cuticularised ; inner and lateral walls are thin. There are large thin-walled water-storing cells with outer and inner walls convexly arched outwards and inwards respectively, intercalated amongst the ordinary epidermal cells in G. Burhia fig. 100 and H. latebrosa fig. 99. The toothed condition of the outer walls in A. vaginalis may be the result of the arrest of parenchyma owing to the deficiency of water. Papillose differentiation of the outer walls js rare, Inner walls in P. trilobus are gelatinised, Stomata are depressed and are found equally numerous on both the surfaces of the leaf when it is isobilateral, or are more numerous on the lower surface when it is bifacial. Stomata are surrounded by ordinary epidermal cells.

The mesophyll is isobilateral in G. Bitrhia fig. 100, species of Indigofera figs. 104, 106 and P. odorata fig. 108. It is bifacial in H. latebrosa, G. medicaginea, A. vaginalis, P. trilobus and species of Rhyncosia. The chief character of the mesophyll is the occurrence of large cells, distinguished by shape and contents in the middle of the mesophyll ; they hold tanniniferous contents and are especially prominent in species of Indigofera figs. 104, 106, Tephrosia and Rhyncosia. In species of Crotalaria, Psoralea and Alysicarpns there is a layer of large polygonal cells in the middle, poor in chlorophyll and perhaps occasionally serving as an aqueous tissue. P. trilobus does not possess any differentiated layer of cells in the middle of the mesophyll.

The isobilateral arrangement of the palisade tissue is common and spongy parenchyma, when present on the abaxial side, is scantily provided with intercellular spaces. The reduction of the ventilating system in the mesophyll is a proof of the xerophytic nature of the plant.

Internal secretory organs are represented by tannin sacs. They occur in the middle of the mesophyll in I. cordifolia and in species of Tephrosia and Rhyncosia and in the palisade tissue in I. paucifolia and P. trilobus. In species of Crotalaria and Psoralea tannin sacs are very few and occur in the neighbourhood of the veins. Tannin sacs are not found in species of Heylandia and Alysicarpns. Sec- tions of the leaf of C. medicaginea were found to be mucilaginous while changing them from lactic acid to glycerine ; this may suggest the presence of mucilaginous cells in the mesophyll.

P. odorata is characterised by the occurrence of intercellular secretory receptacles, termed intramural glands. They occur close beneath the epidermis in the palisade tissue and are bounded towards the palisade tissue by a sheath of cells closely fitting together. The space is traversed by a number of narrow tubular secretory cells, curved more or less like meridians. The external walls of these cells are thickened and take part in the formation of the surface of the leaf. Intramural glands are much more numerous on the lower surface than on the upper.

Oxalate of lime is not found in any form in any of the members.

The veins are embedded in species of Crotalaria and Indigofera ; they are vertically transcurrent above and below by means of collenchyma in P. trilobus, by selerenchyma in species of Heylandia, Tephrosia, Aly sicar pus an d Rhyncosia. The veins are few and do not anastomose freely, which suggests that the leaves do not transpire vigorously.

The hairy covering consists of clothing and glandular hairs. Clothing hairs are of the nature of uniseriate trichomes and have varied forms as follows : —

(a) With walb smooth or muriculate as in H. latcbrosa, C. Burhia fig. 100 and species of Tephrosia, Phaseolus and Rhyncosia.

(b) Terminal cell bent in the form of a hook in A. vaginalis fig. 110.

(c) Terminal cell bent and lying parallel to the surface and with a muriculate surface in P. odorata fig. 108.

{d) Two-armed and formed of a stalk cell and of an unicellular two-armed terminal cell, the arms being equal in species of Indigo/era fig. 105.

The covering of clothing hairs in isobilateral leaves is not dense and it should be noted that two-armed hairs in Indigo/era, though few in number, are short-stalked and form a suitable light screen close to the surface of the leaf, against strong light and glare, which accelerates transpiration and is injurious to chlorophyll.

External glands are not found on the leaf of species of Heylandia, Crotalaria, Indigofera and Tephrosia. In species of Rhyncosia glandular hairs are formed of a short uniseriate stalk and of a spherical head fig. 114 ; they occur on both the surfaces. External glands in P. odorata and P. trilobus are club-shaped and consist of a short uniseriate stalk and of a head divided by horizontal and vertical walls. Glandular hairs in A. vaginalis are composed of a stalk-cell and a globose head, divided by horizontal and vertical walls ; they occur only on the lower surface of the leaf.

It should be observed that external glands are found in a small number of species and sometimes only on the lower surface.

Structure of the Axis: — The epidermis is two-layered in species of Heylandia, Crotalaria and Psoralea; it is single layered in species of Indigofera, Tephrosia, Phaszolus, Alysicarpus and Rhyncosia. The outer walls are thickened and are arched convexly outwards.

Hairy covering has the same character as of that on the leaf. It should be noted that glandular hairs formed of a multicellular stalk and of an irregularly divided head are found in I. argentea.

Internal secretory organs are represented by tannin sacs. They are abundant in species of Indigofera and occur in the cortex and pith. Some of the vessels in I. liniflolia also hold tanniniferous contents. Tannin sacs occur in the soft bast of species of Psoralea and Rhyncosia. Primary cortex is characterised by assimilatory tissue and collenchyma. The assimilatory tissue is formed of palisade cells in C. Burhia ; in others it is chlorenchymatous. The collanchyma is developed in the ribs of the ribbed axis. Eibs are strengthened by sclerenchyma in I. anabaptista, P. odorata and P. trilobus. Cork was not developed in any of the species examined. The endordemis, when differentiated, consists of tabular cells.

The pericycle is composed of a composite ring of bast fibres in species of Heylandia, Indigo/era, Psoralea and Phaseolus. It forms a composite ring of stone-cells in species of Crotal aria, Tephrosia, Alysicarpus and Bhyncosia. In species of Heylandia and Phaseolus groups of bast fibres are developed along three-fourth of the circum- ference of the axis, while along the remaining portion the pericycle is parenchymatous. This is curious and suggests that the axes are much inclined and that sclerenchyma is developed only on the upper side of the inclined axis. Small groups of bast fibres occur in soft bast of Alysicarpus vaginalis.'

The perforations of vessels are simple. Size of lumen, abundance and arrangement of the vessels vary in different genera and even in species. These differences may be useful in diagnosis of genera and species, if- due allowance is made for modifications introduced by con- ditions of the soil.

The vascular system, as a whole, is characterised by the poor development of vessels as regards size and abundance, by abundance of wood prosenchyma and by poorly developed wood parenchyma. These modifications are due to the arrest of the development of parenchyma owing to deficiency of water. A system of well developed water conducting tissue is not required in the axis of desert plants in which all structures are adapted to diminish transpiration. It should be observed that the size and abundance of vessels are usually inverse- ly proportional to each other.

Soft bast usually forms a continuous ring. It is characterised by the occurrence of tannin sacs in species of Indigo/era, Psoralea and Bhyncosia and by the presence of small groups of bast fibres in A. vaginalis.

Pith consists of thin-walled cells in species of Heylandia and Crotalaria, I. linifolia, I. argentia, species of Tephrosia, A. vaginalis, P. tribolus and B. arenaria ; and is formed of thick-walled and lignified cells in I. paucifolia, I. anabaptista, P. odorate and B. rhombifolia. Some of the pith cells in I. paucifolia and I. argentia hold tanninifer- ous contents. The pith composed of lignified cells adds to the rigidity afforded by the mechanical tissue ; when it is formed of thin-walled cells it may serve occasionally as an aqueous tissue. Page:The Journal of Indian Botany.djvu/285 Anomolous structures are represented by cortical vascular bund- les in C. Burhia, fig. 101.

General Review

Outer walls of the epidermal cells are thickened and cuticuiarised. Spongy tissue is greatly diminished and the ventilating system is greatly reduced. Water-storing tissue is extensive in the leaf and occurs either in the epidermis or in the palisade tissue, or in the middle of the mesophyll. Tannin sacs are abundant. Secretory cavities are represented by intramural glands in Psoralen odorata. Oxalate of lime is not found in the leaf or axis. The system of veins is poorly developed. Clothing hairs are never unicellular ; they are uniseriate trichomes, either simple, or hooked, or armed. Glandular hairs are either club-shaped or spherial and are not abundant.

The pericyle forms a composite ring either of groups of bast fibres or of stone-cells. Vessels have simple perforations and are not numer- ous. Inter fascicular wood prosenchyma is abundantly developed forming the ground work of the vessels. Wood parenchyma is poorly developed. Medullary rays are usually uniseriate and numerous.

The pith consists of thin-walled or thick-walled and lignified cells.

Anomelous structures are represented by cortical vascular bundles in 0. burhia.

CAESALPINEAE

Cassia obovata, Goliad.— Figs 118,119. Epidermal cells with outer walls papillose. Stomata occurring on both the surfaces. Mesophyll isobilateral. Veins embedded. Clothing hairs unicellular. Assimilatory tissue formed of chlorenchyma. Vessels large. Medullary rays uniseriate. Pith formed of cells with thickened and lignified walls.

Structure of the Leaf : — The epidermal cells have outer walls drawn out into large papillage, fig. 118. The stomata are equally numerous on both the surfaces. Guard-cells are situated in the plane of surrounding cells ; and the front cavity is placed in a deep depres- sion formed by the outer papillose epidermal walls.

The mesophyll is isobilateral. The palisade tissue on the adaxial side consists of longer cells than those on the lower surface with transversely elongated cells between. The veins are embedded. The large veins are protected above and below by sclerenchyma ; the smaller ones have large strands of sclerenchyma only on the lower side. Hairy covering consists of unicellular curved hairs with perhaps a function of absorbing water. Walls are thin and superficially knobbed. Glandular hairs are not found in the leaf and axis.

Structure of the Axis : —The epidermal cells are small with outer walls thickened and papillose. The primary cortex is formed of chlorenchyma.

The perioycle forms a more or less composite ring of stone- cells. The wood is composite. Vessels are large and few ; they are more abundant in the inner half of the wood. Interfascicular wood prosenchyma is extensive. Wood parenchyma is more abundantly developed than in Papilionaceae and enclose the inner ends of the xylem bundles. The medullary rays are unseriate.

The pith consists of small cells with thickened and lignified walls.

MIMOSEAE

Acacia Senegal, Willd. —Figs, 120, 121. Epidermal cells with outer walls thickened and papillose. Stomata occurring on both the surfaces. Mesophyll formed of palisade tissue on the upper side and of arm-palisade tissue on the lower. Tannin sacs present in the leaf and axis. Veins embedded. Clothing hairs unicellular. Cork subepider- mal. Pericycle forming a composite ring of stone-cells. Small groups of stone-cells in soft bast. Vessels large. Medullary rays uniseriate. Pith composed of cells with thick and lignified walls.

Structure of the Leaf: — The epidermal cells have outer walls thickened and papillose. Stomata occur on both the surfaces. The guard-ceils are situated in the plane of surrounding cells and the front cavity is placed in a depression formed by the papillose outer walls of the epidermal cells.

The mesophyll is composed of 3-4 layers of palisade cells on the adaxial side and of arm-palisade tissue on the abaxial side. The middle tissue consists of a layer of large parenchymatous cells with tanniniferous contents. Internal secretory organs are represented by tannin sacs occurring in the middle of the mesophyll, in cortex and pith.

The veins are embedded. The veins of the mid-rib are protect- ed on the lower side by strands of sclerenchyma.

The hairy covering consists of a few unicellular clothing hairs. Glandular hairs are not found.

Structure of the Axis: — The cortex is characterised by subepi- dermal cork. Some of the cells of the tanniniferous cortical parenchyma near the pericyclic stone-tissue contain solitary crystals of oxalate of lime. The pericycle forms a more or less composite ring of stone-cells. Small groups of stone-cells occur in the soft bast. The wood is compo- site. Vessels are large and are arranged in incomplete rows. Inter- fascicular wood prosenchyma is extensive and is composed of small thick-walled cells with small lumina. The medullary rays are unis- eriate. Wood parenchyma is little developed.

Pith is composed of small cells with thickened and lignified walls.

ROSACEAE

Neurada procumbens L . — Figs. 122, 123, 124.— Epidermal cells tabular with outer and inner walls thickened and convexly arched outwards and inwards respectively. Stomata found on both the surfaces and accompanied by ordinary epidermal cells. Hairs uncellular and wooly. External glands absent. Mesophyll composed wholly of short palisade cells. Internal secretory cells with mucila- ginous membrances on all sides and occurring near the veins in the leaf, and in collenchyma, cortical parenchyma, medullary rays and pith of the axis. Epidermal cells with tanniniferous contents. Leaves many ribbed. Smaller veins embedded. Larger veins vertically trans- current by collenchyma. Epidermal cells of the axis with outer- walls papillose. Medullary rays broad. Interfascicular wood prosen- chyma absent. Pith composed of thin-walled cells. Pith cells with mucilaginous walls towards the periphery.

Structure of the Leaf: — The epidermis consists of tabular cells with outer and inner walls convexly arched outwards and inwards respectively. Lateral walls are thin and straight. Epidermal cells hold tanniniferous contents. The stomata are more numerous on the lower surface and are surrounded by ordinary epidermal cells. The guard-cells are situated in the plane of surrounding cells and the front cavity is placed in a depression formed by the outer thickened epidermal walls fig. 123. The stomata on the axis are similar to those on the leaf.

The mesophyll is wholly composed of short palisade cells fig. 122. Internal secretory organs are represented by cells with mucilaginous membranes on all sides and by epidermal cells of the leaf with tanniniferous contents. Cells with mucilaginous membranes occur near the veins, at the inner margin of cortex, in the medullary rays and in the pith tissue towards the periphery. Tanniniferous contents in the epidermal cells of the leaf give an acrid taste to foliage leaves and prevent them from being easily devoured by animals.

Oxalate of lime is found in the form of numerous small clustered crystals near the veins of the leaf and in collenchyma and soft bast of the axis. The leaves are many ribbed, the ribs being prominent beneath and grooved above. The smaller veins are enclosed in a sheath of cells, some with mucilaginous membranes and others with clustered crystals. The larger veins are vertically transcurrent above by coilenchyma.

The hairy covering is dense and consists of clothing hairs on the leaf and axis. The clothing hairs are unicellular, long and woolly figs. 122, 124 ; they are more numerous on the lower surface of the leaf.

Structure of the Axis : — The epidermis consists of polygonal cells with outer walls thickened and papillose. The inner walls are thick- ened ; the lateral walls are thin and undulated.

The cortex fig. 124 is composed of coilenchyma on the outer side and of an extensive tissue of thin-walled colourless cells on the inner side with perhaps occasionally a water-storing function. Cells at the inner margin of the cortex have mucilaginous membranes.

Sclerenchymatous pericycle is not developed. The wood is com- posed of large xylem bundles separated by broad medullary rays some of the cells of which have mucilaginous membranes. Interfasci- cular wood prosenchyma is not developed.

The pith cells towards the periphery are mucilaginous.

LYTHRACEAE

Ammania baccifera L. — Fig. 125. Epidermis formed of thin- walled tabular cells. Clothing hairs absent. Oxalate of lime not found. Pericycle formed of bast fibres, with thin walls and large lumina. Small groups of thick-walled cells found in the pith formed of thin-walled cells.

Ammania desertorum Blatt. & Hall— Fig. 126. Epidermal cells tabular with outer walls thickened and convexly arched outwards. Clustered crystalls found near the veins. Conical unicellular hairs with verrucose walls occurring on the axis and on the upper surface of the leaf. Pericycle formed of bast fibres with thick walls and with small lumina. Pith composed of thin- walled cells.

Structure of the Leaf : — The epidermal cells in A. baccifera fig. 125 are tabular and thin-walled except at the margin where the outer walls are thickened and convexly arched outwards. In A. desertorum the epidermal cells have the outer walls thickened and convexly arched outwards. The cuticle is striated. The lateral walls are thin and straight. The margins are curved downwards.

Stomata are more numerous on the lower surface and are surrounded by ordinary epidermal cells. Guard-cells are elevated and the front cavity is on a level with the surface figs. 125, 126. The stomata on the axis are similar to those on the leaf.

{To be continued)

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