# The Journal of Indian Botany/Volume 2/June 1921/The Physiological Anatomy of the Plants of The Indian Desert

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​THE Journal of Indian Botan-p. Vol. II. JUNE, 1921. Nos. 4 & 5.
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. 73.)
SCROPHULARIACEAE.
Anticharis linearis Hochst— Fig. 245 (Axis only). Epi- dermal cells tabular. Cuticle smooth. Guard-cells elevated. Trie- homes straight and smooth-walled. Cells of the outermost layer of cortex showing collenchymatous differentiation. Pericycle forming a loose ring of groups of bast fibres. Wood-ring broad. Vessels small and arranged in incomplete long rows. Interfascicular wood pro- senchyma extensive and formed of cells with thick walls and with small lumen. Medullary rays uniseriate and numerous. Pith of thin-walled cells.
Schweinfurthia sphaerocarpa Braun.— Figs. 246, 247. Epi- dermal cells of the leaf and axis tabular. Large conical unicellular knobbed hair-like structures intercalated amongst ordinary epidermal cells. Cuticle striated. Trichomes curved and with walls covered with cuticular knobs. Mesophyll bifacial. Guard-cells elevated. Stomata on both the surfaces. Cells of the outermost layer of cortex showing collenchymatous differentiation. Pericycle in the form of isolated bast fibres. Wood-ring narrow. Vessels large and arranged in complete rows. Medullary rays absent. Interfascicular wood prosenchyma little developed and composed of cells with thin walls and large lumen. Pith of thin-walled cells.
Structure of the Leaf.— The epidermis in S. sphaerocarpa (fig. 246) consists on both sides of tabular cells with the outer walls greatly CM ​thickened and convexly arched outwards. There are large unicellular conical hair-like structures, with walls covered with cuticular knobs, intercalated amongst ordinary epidermal cells (fig. 246). The lateral walls are thin and undulated. The inner walls are thin. The cuticle is striated. The stomata are equally numerous on both the surfaces and are surrounded by ordinary epidermal cells. The guard-cells are elevated and the front cavity is on a level with the surface.
The mesophyll is bifacial. Internal secretory organs and oxalate of lime are not found. The veins are embedded and are not enclosed in bundle-sheaths. The hairy covering on the axis consists of thin- walled uniseriate trichomes. Trichomes in S. sphaerocarpa are covered with cuticular knobs. Large conical epidermal cells with walls covered with cuticular knobs (figs. 246, 247) may be of the nature of unicellular hairs in S. sphaerocarpa- The trichomes in A. linearis are smooth-walled and straight. Glandular hairs are not found.
Structure of the Axis. — Epidermis consists of tabular cells with outer walls greatly thickened and convexly arched outwards. Cuticle is striated. There are large concical unicellular hair-like structures with walls covered with cuticular knobs intercalated amongst ordinary epidermal cells in S. sphaerocarpa (fig. 247). Lateral walls are thin and straight. The stomata are like those on the leaf. The cortical parenchyma is composed of horizontally elongated cells. The cells of the outermost layer of the cortex show collenchymatous differentiation at angles in contact with the epidermal cells.
The pericycle consists of a few isolated bast fibres and of a loose ring of groups of bast fibres in S. sphaerocarpa (fig. 247) and A. linea- ris (fig. 245J respectively. The wood forms a composite hollow cylinder. The vessels in S. sphaerocarpa (fig. 247) are arranged in com- plete rows ; interfascicular wood prosenchyma is little developed and is composed of cells with thin walls and with large lumen. The vessels in A. linearis are small and are arranged in long incomplete rows ; the interfascicular wood prosenchyma is extensive and is composed of cells with thick walls and with small lumen. The medullary rays are uniseriate and numerous in A. linearis; they are absent in S. sphaerocarpa. The pith is composed of thin-walled cells.
ACANTHACEAE.
Blepharis sindica T. Anders.— Figs. 248, 249, 250. Outer walls of epidermal cells greatly thickened. Guard-cells elevated. Front cavity on a level with the surface. Mesophyll formed of palisade tissue on the upper side and of subepidermal aqueous tissue and palisade tissue on the lower. Veins provided with bundle-sheaths. ​Clothing hairs unicellular and conical. Glandular hairs formed of a stalk-cell and of a spherical head divided by horizontal and vertical walls. Crystal sand in the clothing hairs of the leaf and in epidermal cells of the axis. Collenchyma forming a continuous ring. Aqueous tissue occurring below collenchyma. Pericycle in the form of isolated bast fibres. Vessels uniformly distributed in the wood-ring. Inter-fasciculer wood prosenchyma fairly extensive. Wood parenchyma fairly extensive- Medullary rays few and uniseriate. Pith of thin- walled cells.
Ruellia patula J acq.— Fig. 251. Guard-cells elevated. Front cavity on a level with the surface. Mesophyll of palisade tissue on the upper side and of arm-palisade tissue on the lower. Veins not provided with bundle-sheaths. Clothing hairs uniseriate and more or less jointed. Glandular hairs with an uniseriate stalk and with a disc-shaped head divided by horizontal and vertical walls. Assimilatory tissue in the axis parenchymatous. Structures resembling internal glands found in cortex. Pericycle of a few isolated bast fibres. Wood composed of large bundles at the angles and connected by strands of interfascicular wood prosenchyma. Wood parenchyma in groups on the inner side of xylem bundles. Medullary rays uniseriate. Pith of thick-walled cells.
Barleria hochstetteri Nees — Figs. 252, 253, 254, 255, 256, 257. Guard-cells in the plane of surrounding cells. Mesophyll isobilateral. Veins without bundle-sheaths. Structures resembling internal glands present. Clothing hairs on the leaf short and unicellular, and those on the axis in the form of armed trichomes. Glandular hairs with an uniseriate stalk and with a disc-shaped head divided by a vertical wall. Collenchyma strengthening the ribs. Assimilatory tissue in the axis parenchymatous. Sclerenchymatous pericycle not developed. Vessels uniformly distributed in the wood-ring. Wood narrowed at two opposite points. Medullary rays uniseriate. Interfascicular wood prosenchyma little developed. Pith of thin-walled cells and retained. Pith cells with acicular or rod-like crystals. A thick-walled vessel present in pith.
Justicia simplex Don.— Fig. 258, 259. Guard-cells elevated or in the plane of surrounding cells. Mesophyll isobilateral. Structures resembling internal glands found in the mesophyll. Veins without sheaths. Clothing hairs short and uniseriate. Glandular hairs with a stalk-cell and with a spherical head divided by horizontal and vertical walls. Assimilatory tissue in the axis formed of palisade cells. Collen- chyma developed at the angles of the quadrangular axis. Scleren- chymatous pericycle not developed. Wood composed of xylem bundles at the angles connected by strands of interfascicular wood pro​senchyma. Wood parenchyma developed on the inner side of the xylem bundles. Medullary rays absent. Pith of thin-walled cells.
Structure of the Leaf. — The epidermis consists of polygonal cells in B. patula, B. hochstetteri and J. simplex or of tabular cells as in B. sindica. The outer walls are thickened, thickening being considerable in B. sindica. Tne outer walls are convexly arched outwards and the lateral walls thin and undulated in J. simplex. The cells are uniformly thickened on all sides in B. patula and B. hochstetteri ; the lateral walls are undulated. The lateral and inner walls are also thickened in B. sindica and the latter are undulated.
Numerous large rounded cells are intercalated amongst ordinary epidermal cells ; and each contains a spherical cystolith (fig. 258), The stomata are accompanied by subsidiary cells. The guard-cells are usually elevated and the front cavity is on a level with the surface in all members except B. hochstetteri in which the guard-cells are in the plane of surrounding cells and the front cavity is a little depressed. The stomata are more numerous on the lower surface except in B. sindica where they are more numerous on the upper surface. This may be accounted for by the occurrence of subepidermal aqueous tissue on the lower side where there should be as few stomata as possible to economise the supply of water contained in the aqueous tissue. The mesophyll is isobilateral except in B. patula in which it consists of palisade tissue on the adaxial side and of arm-palisade tissue on the abaxial side. In B. sindica there is palisade tissue on the adaxial side and subepidermal aqueous tissue and palisade tissue on the abaxial side.
In B- hochstetteri and J. simplex there are peculiar structures on both sides of the mesophyll. They are at some places circular in section and are composed of irregular cells faintly green in colour ; at other places they have the form of secretory cavities with bounding cells projecting into them (fig. 258). These structures probably represent the internal secretory organs. Oxalate of lime does not occur in the form of crystal sand in the cell-cavity of clothing hair8 on the leaf and in the epidermal cells of the axis of B. sindica. The veins are embedded and are not enclosed in bundle-sheaths.
The hairy covering on the leaf and axis consists of clothing and glandular hairs. The clothing hairs in B. patula (fig. 251) and J. simplex (fig. 258) are simple uniseriate trichomes with thickened and muriculate walls ; the constituent cells in the former are dilated at the lower end and give a jointed appearance to the trichomes. In B. hochstetteri there are unicellular elliptical hair-like structures with walls thickened and muriculate on the leaf ; on the axis, besides the long simple uniseriate trichomes (fig. 255), there are other special ​forms which consist of a stalk-cell and of a terminal cell which is unicellular and two-armed and sometimes with a small scale on its upper side (figs. 256, 257). The walls of these different forms of hairs in B. hochstetteri are muriculate. The clothing hairs in B. sindica (fig. 249) are unicellular and conical and have walls thickened and muriculate.
External glands occur on the leaf and axis of all members. In B. sindica, B. patula and J. simplex they are placed in epidermal depressions and consist of a stalk-cell and of a spherical head divided by horizontal and vertical walls (fig. 258). Glandular hairs on the axis of B. patula and on the leaf and axis of B. hochstetteri, consist of a long uniseriate stalk and of a disc-shaped head divided either by a vertical walls (figs. 253, 255) or both by horizontal and vortical walls. Structure of the Axis. — The epidermal cells are tabular in B. sindica and J. simplex ; they are polygonal in B. hochstetteri and B. patula. The outer walls are thickened. There are numerous large cells, circular in T. S., intercalated amongst ordinary epidermal cells, each containing a rounded cystolith (fig. 251). The stomata on the axis are like those on the leaf. The stomata situated on the sides of furrows in B. hochstetteri, however, are elevated a good deal above the epidermis.
The primary cortex is characterised by the occurrence of collenchyma which forms larger groups at the angles and smaller ones between them. The collenchyma in B. sindica forms a continuous ring. The assimilatory tissue in B. patula and B. hochstetteri is formed of chlorenchyma, while in J. simplex it consists of large thin-walled cells which occasionally act as water-reservoirs.
Sclerenchymatous pericycle is not developed except in B. sindica and B. patula, in which it consists of isolated bast fibres The wood is composite in all members; it is of uniform breadth except in B. patula, in which it is much narrowed at two opposite points. The wood in B. hochstetteri and J. simplex, is composed of large xylem bundles at the angles connected by strands of interfascicular wood prosenchyma with a few rows of vessels embedded in them. The vessels in B. sindica and B. patula are uniformly distributed in the interfascicular wood prosenchyma. The narrowed portions of the wood-ring represent the plane at right angles to the direction of the wind. The medullary rays are uniseriate. They are numerous in B. hochstetteri. The wood parenchyma is little developed in B. sindica and B. hochstetteri while in B. patula and J. simplex it occurs in groups on the inner side of the angular xyem bundles.
The pith is composed of thin-walled cells except in R. patula in which it consists of thick-walled cells. Oxalate of lime is found in ​the form of bundles of acicular or rod-like crystals in the pith cells of B. hochstetteri. Anamolous structures are represented by isolated thick-walled vessels in the pith of B. hochstetteri.
General Revieiu. — Epidermal cells have the outer walls thickened. There are large cells, containing rounded cystoliths, intercalated amongst ordinary epidermal cells. The stomata are accompanied by subsidiary cells. Mesophyll is either isobilateral or is composed of palisade tissue on the upper and of arm-palisade tissue on the lower side. Structures resembling internal glands are found in the mesophyll of some members. Oxalate of lime is found only in the pith cells of B. hochstetteri, in the form of bundles of acicular or rod-like crystals. Besides simple unicellular hairs or uniseriate trichomes which are of general occurrence, there are special forms of trichomes such as armed trichomes on the axis of B hochstetteri. External glands are found in all members. The assimilatory tissue in the axis is composed of chlorenchyma or of palisade cells. The collenchyma either forms groups or is found in the form of a more or less continuous ring, below the epidermis. An aqueous tissue is found in the leaf and axis of B. sindica. Sclerenchymatous pericycle occurs only in B. patula, in the form of isolated bast fibres. The wood forms a composite ring. The interfascicular wood prosenchyma is fairly extensive in members in which the vessels are not uniformly distributed. The pith consists of thin-walled or thick-walled cells. Anamolous structures are represented by thick-walled vessels in the pith of B. hochstetteri.
VERBENACEAE.
Boucbea marrubifolia Schemer.— Figs. 260, 261, 262. PI. XXVI. Epidermal cells tabular with outer walls very greatly thickened. Guard-cells accompanied by two subsidiary cells. External glands composed of a uniseriate stalk and of an elliposidal bicellular head. T. S. of the axis quadrangular. Pericycle formed of groups of the stone-cells. Cork absent.
Cleredendron Phlomidis L./.— Figs. 263, 264. Epidermal cells tabular with outer and inner wall equally a little thickened. Guard-ceils accompanied by 4-5 ordinary epidermal cells. External glands composed of a stalk-cell and of a broad elliptical head divided by many vertical walls. Pericycle forming a loose ring of stone-cells. Cork developed below collenchyma. T. S. of the axis circular.
Structure of the Leaf. — The epidermal cells are tabular with the outer and inner walls thickened, the thickening of the outer walls being considerable in B. marrubifolia (fig. 260). The lateral walls ​are thin and straight. The stomata occur on both the surfaces and are accompanied by subsidiary cells in B marrubifolia and by 4 or 5 ordinary epidermal cells in C. Phlomidis. The guard-cells are a little elevated and the front cavity is placed in depressions formed by thickened outer epidermal cells.
The mesophyll is composed of palisade tissue on the upper side and of arm-palisade tissue on the lower. Internal secretory organs and oxalate of lime are found neither in the leaf nor in the axis. The veins are embedded and are not provided with bundle-sheaths.
The hairy covering on the leaf and axis consists of clothing and glandular hairs. Clothing hairs occur in the form of unicellular or bluntly pointed uniseriate trichomes with muriculate walls. The clothing hairs are more numerous on the lower surface. The glandular hairs are placed in epidermal depressions. They are composed in C. Phlomidis of a stalk-cell and of a broadly disc-shaped head divided by many vertical walls (fig. 264). In B. marrubifoli (fig. 262), they consist of a short uniseriate stalk and of a disc-shaped head divided by an oblique wall.
Structure of the Axis.—The epidermal cells are tabular, with outer walls thickened and muriculate in B. marrubi/olia, and thin and convexly arched outwards in C. Phlomidis. The lateral walls are thin and straight. The primary cortex is composed on its outer side of collenchyma and on its inner side of cortical parenchyma. Cork is developed below the collenchyma in C. Phlomidis. Cortical parenchyma is of uniform breadth in G. Phlomidis and is more extensive in the plane exposed to the wind in B. marrubifolia.
The pericycle consists of a more or less composite ring of stone-cells in G. Phlomidis and of groups of stone-cells in B. marrubifolia. The stone-cell tissue is more extensive in the plane exposed to the wind in B. marrubifolia. The wood forms a composite hollow cylinder. The vessels are large and are uniformly distributed in incomplete rows in the extensive interfascicular wood prosenchyma. Medullary rays are 1-2 seriate and are numerous.
The pith consists of thin-walled cells.
LABIATAE.
Salvia aegyptiaca L—Figs. 265, 266, 267. Upper epidermal cells larger. Epidermal cells tabular with outer walls very greatly thickened. Stomata on both the surfaces and accompanied by subsidiary cells. Mesophyll formed of palisade tissue on the upper and of arm-palisade tissue on the lower. Internal glands and oxalate of ​lime absent. Veins without bundle-sheaths. Clothing hairs uniseriate trichomes. Glandular hairs spherical. Epidermal cells of the axis with outer and inner walls thickened. T. S. of the axis quadrangular. Collenchyma in the angles. Pericycle of stone-cells groups. Assimilatory tissue in the axis of palisade cells. Endodermis differentiated and with radial walls suberised. Wood composite. Interfascicular wood prosenchyma extensive and composed of cells with thick walls and with small lumen. Medullary rays uniseriate. Pith of thin-walled cells.
Structure of the Leaf.—The epidermis consists of tabular cells with the outer walls very greatly thickened. The cells on the upper side are larger than those on the lower. The lateral walls are thin and straight.
The stomata occur on both the surfaces and 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 mesophyll is composed of palisade tissue on the upper side and of arm-palisade tissue on the lower. Internal glands and oxalate of lime do not occur in the leaf or axis. The veins are not enclosed in bundle-sheaths. The leaves are many-ribbed. The veins of the ribs are vertically transcurrent above and below by colourless parenchyma.
The hairy covering on the leaf and axis consists of clothing and glandular hairs. Clothing hairs are in the form of uniseriate trichomes with verrucose walls (fig. 266). They are more numerous on the lower surface. The trichomes on the axis are much longer; but are otherwise like those on the leaf (fig. 267). External glands occur in two forms on the leaf and axis. They either consist of a short uni-seriate stalk and of a spherical unicellular head, or are formed of a stalk-cell an3 of a bladder-like head the cuticle of which is raised like a bladder, owing to the accumulation of secretion.
Structure of the Axis.—The T. S of the axis is quadrangular in outline with shallow grooves between the angles. The epidermis consists of small tabular cells with the outer and inner walls thickened. The outer walls are convexly arched outwards. The internal walls are thin and straight. The cuticle is thick. The cortex (fig. 267) is characterised by subepidermal strands of collenchyma situated in the angles. The assimilatory tissue consists of strands of palisade cells between the collenchyma at the angles. The endodermis is distinct and consists of thin-walled cells with radial walls suberised.
The pericycle is composed of groups of stone-cells at the angles (fig. 267). The wood is composed of large xylem bundles at the angles and of small ones between fchem. The interfascicular wood ​prosenchyma is extensive and is composed of thick- walled cells with small lumen. The medullary rays are uniseriate and numerous. Wood parenchyma is little developed.
The pith consists of thin-walled cells.
NYCTAGINACEAE.
Boerhaavia diffusa L— Figs. 268, 269. Upper epidermis of cubical cells. Lower epidermis of tabular cells. Epidermal cells of the leaf and axis with tanniniferous contents. Palisade tissue on the upper side and round the veins. Aqueous tissue below lower epidermis. Veins with thick-walled green sheaths. Glandular hairs with a uniseriate stalk and with an ellipsoidal head. Epidermal cells of the axis polygonal. Pericycle formed of isolated bast fibres. Endodermis of thick-walled tabular cells.
Boerhaavia verticillata Puir.— Epidermis of both sides of tabular cells. Mesophyll bifacial. Glandular hairs absent. Veins without bundle-sheaths. Pericycle forming a loose ring of bast fibres. Endodermis of thin-walled tabular cells.
Boerhaavia elegans Chois.^ Fig. 270. Specific characters al- most the same as those of B. diffusa. From the point of view of anatomical characters it should belong to the same species.
Structure of the Leaf. — The epidermis on the upper side of B. diffusa and B. elegans consists more or less of cubical cells with the outer and inner walls a little thickened. The latter are convexly arched outwards. The lower epidermis in B. diffusa and B. elegans and the epidermis on both sides in B. verticillata consists of tabular cells with the outer walls thickened and convexly arched outwards. The lateral walls are thin and straight in all members. The granula- ted appearance of the outer walls is due to the deposits of crystaline granules of calcium oxalate ; and the granulated walls are covered by a thick cuticle. The occurrence of deposits of calcium oxalate in the epidermal walls of these succulent plants protects them from desiccation as well as from being easily devoured by animals on account of the acrid taste.
Stomata occur on both the surfaces 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 upper portions of surrounding cells.
The mesophyll in B. diffusa and B. elegans is composed of palisade tissue on the upper side and about the veins and of a tissue of thin-walled colourless polygonal cells with probably a water- storing function on the lower side. In B. verticillata palisade tissue ​occurs on the upper side ; and there is an extensive tissue, occupying two-thirds of the portion of mesophyll, of thin-walled polygonal cells faintly green in colour and partly functioning as an aqueous tissue.
Internal secretory organs are represented by epidermal cells, with tanniniferous contents, of the leaf and axis of B. diffusa and B. elegans.
Oxalate of lime, besides being deposited in the form of granules in outer epidermal walls, occurs in the form of bundles of raphides and of crystal sand in mesophyll of leaves and in the primary cortex of the axis of all members. Granular deposits in the outer epidermal walls are abundant and give to the surface of the leaf and axis a whitish appearance, which besides protecting these succulent plants from being easily devoured by animals on account of the acrid taste, reflect light and arrest transpiration.
The veins are embedded and are enclosed in thick-walled green bundle-sheaths in B. diffusa and B. elegans. Bundle-sheaths are not found in B. verticillata.
The hairy covering consists of glandular hairs and occurs on the axis and both the surfaces of the leaf of B. diffusa and B. elegans. The glandular hairs (tig. 268) are composed of a uniseriate long stalk and of an elongated and ellipsoidal head. The cells of the stalk become narrower towards the apex. External glands are not found in B. verti- cillata.
Structure of the Axis. — The epidermal cells in B. diffusa are poly- gonal, while those in B. verticillata are tabular. The outer walls are thickened, convexly arched outwards and granulated with deposits of calcium oxalate. The primary cortex (fig. 269) is composed of collen- chyma on its outer side and of chlorenchyma on the inner side. The endodermis is distinct and is composed of tabular cells which are thick-walled in B. diffusa and B. elegans.
The pericycle consists either of isolated bast fibres as in B. diffusa and B. elegans or of a loose ring of bast fibres in B. verticillata. The wood is characterised by the occurrence of two rings of xylem bundles. The primary bundles are small and are embedded in a thin ring of interfascicular wood prosenchyma which is composed of cells with thick walls and with small lumen. The secondary bundles are irre- gularly arranged in the pith and are separated by broad strips of thin- walled parenchymatous cells, resembling medullary rays. Soft bast is found in groups on the outer side of xylem bundles.
The pith tissue between the primary and secondary vascular bun- dles consists of cells with thickened and lignified walls and filled with granular contents, and that between and enclosed by the secondary vascular bundles is formed of very thin-walled cells. ​
AMARANTACEAE.
Aerua tomentosa Forsk.— Figs.:271, 272, 273, 274. Mesophyll bifacial. Veins with bundle-sheaths. Mid-rib prominent above and below. Clustered crystals in the leaf and axis. A dense covering of candelabra hairs on the leaf and axis. Collenchyma in the angles of the axis. Assimilatory tissue in the axis chloreuchymatous. Pericycle of groups of stone-cells. Pith of thick-walled cells.
Aerua pseudo-tomentosa Blatt. & Ball— Figs. 275, 277, 280, 281. Mesophyll bifacial. Clustered crystals in the leaf and axis. Veins with bundle-sheaths. Mid-rib furrowed above and prominent below. A dense covering of candelabra hairs on the leaf and axis. Assimilatory tissue in the axis formed of palisade cells. Collenchyma in the angles. Pericycle of groups of stone-cells. Pith of thick*walled cells.
Achyranthes aspera L.— Figs. 282, 283, 284. Mesophyll bifacial. Clustered crystals in the leaf and axis. Veins without bundle-sheaths. Clothing hairs in the form of uniseriate trichomes with walls knobbed. Glandular hairs with a uniseriate long stalk and with an ellipsoidal head. Collenchyma in the angles. Assimila- tory tissue in the axis chlorenchymatous. Pericycle of groups of stone-cells and isobilateral. Two vascular bundles in pith. Pith of thin-walled cells.
Pupalia lappacea Moq.— Figs. 276, 278, 279. Mesophyll bifa- cial. Oxalate of lime in the form of clustered crystals in the leaf and that of crystal sand in the axis. Veins without bundle-sheaths. Hairs uniseriate, curved and smooth-walled. Collenchyma in angles. Assimi- latory tissue in the axis chlorenchymatous. Pericycle of groups of stone-cells and isobilateral. Pith of thin- walled cells.
Structure of the Leaf. — The epidermis consists of tabular cells with the outer and inner walls thickened and convexly arched outwards and inwards respectively. The lateral walls are thin and straight. The stomata are more numerous on the lower surface and are surrounded by ordinary epidermal cells. The guard-cells of the stomata on the upper surface are in the plane of surrounding cells and the front cavity is placed in a depression formed by outer thickened epidermal walls (fig. 275). The guard-cells of the stomata on the lower surface are a little elevated and the front cavity is on a level with the surface. The stomata on the axis are placed in depressions formed by outer thickened epidermal walls. The stomata are replaced by lenticels in the rhizomatous axes of A. tomentosa.
The mesophyll is composed of palisade tissue on the upper and of spongy tissue on the lower. Oxalate of lime occurs in the form of ​large clustered crystals in the neighbourhood of veins of all members and in the cortex and pith of both species of Aerua and in A. aspera. In the rhizomatous axis of A. tomentosa numerous clustered crystals are present in the neighbourhood of water-storing tracheids, in many of the medullary ray cells and in the pith. In the axis of P. lappacea oxalate of lime is found in the form of crystal sand composed of triangular granules in the cortex and pith.
The veins are embedded except those of the mid-rib which are vertically transcurrent above and below by collenchyma. They are enclosed in bundle-sheaths of thick-walled green cubical cells in both the species of Aerua. The mid-rib is furrowed above and prominent below in A. pseudo-tomentosa, while in A. tomentosa it is prominent above and below.
The hairy covering (fig. 277) in the leaf and axis of both the species of Aerua consists of a dense covering of candelabra hairs which are more numerous on the lower surface. The underground rhizomatous axis of A. tomentosa is quite glabrous. Clothing hairs in A. aspera occur in the form of uniseriate trichomes composed of a few basal cells and of a long terminal cell curved as on a hinge. Walls are characterised by warts by means of which the hairs dove- tail with one another and form a dense covering (fig. 282). Besides clothing hairs, there are external glands composed of a uniseriate stalk and of an ellipsoidal head (fig. 283). Uniseriate trichomes in P. lappacea (fig. 279) are smooth-walled and consist of a basal portion of a few short cells and of a terminal portion which is curved and is composed of longer and jointed cells. The clothing hairs are filled with air and become white ; they thus reflect light and glare and arrest transpiration.
Structure of the Axis. — The epidermis consists of small tabular cells with outer and inner walls thickened and convexly arched out- wards and inwards respectively. The primary cortex is characterised by collenchyma at the angles and by an assimilatory tissue which is composed of palisade cells in A. pseudo-tomentosa and of chlorenchyma in other members. In the rhizomatous axis of A. tomentosa the assimilatory tissue is not developed. The assimilatory tissue in P. lappacea, forms a continuous ring, while in other members it occurs between collenchyma groups at the angles. There is a layer of green cells resembling the cells of the bundle-sheath, close below the assimilatory tissue of both the species of Aerua.
There is extensive development of cork in the rhizomatous axis- of A. tomentosa. It extends between epidermis and pericycle and also between the latter and the groups of soft bast. It is partly of epidermal and partly of pericyclic origin. ​ The pericycle in both the species of Aerua consists of long thin groups of stone-cells. In the rhizomatous axis of A. tomentosa it forms a composite ring of stone-cells except at certain spots where stone-cells are not developed and where the space is occupied by the conjunctive tissue of medullary rays, which is very extensive where the gaps are large. Sometimes lenticels are found above these gaps ; it may therefore be supposed that this conjunctive tissue forms a system of communication between the lenticels and the vascular tissue.
In P. lappacea the stone-cell groups of the pericycle are trian- gular. The bases of these groups on two opposite sides of the axis are lengthened out, so that adjacent groups unite and form composite strands, while on the other two sides the stone-cell groups are isolated, the pericycle thus presenting an isobilateral symmetry. In A. aspera a similar isobilateral arrangement is presented, but in a different way. The stone-cell groups on two opposite sides of the axis are longer and thinner than those on the other two. The isobilateral symmetry of pericycle may have been developed by the direction of the prevailing wind, the more composite structure being developed in the plane more affected by the wind.
The wood forms a composite ring. The interfascicular wood prosenchyma is much more extensive and is composed of cells with much more thickened walls and with much smaller lumen, in both the species of Aerua than in the case of A. aspera and P. lappacea. In P. lappacea the arrangement of xylem bundles is isobilateral, larger bundles being developed below the composite stone-cells strands and smaller ones below isolated stone-cell groups. This suggests that functional activity is greater on these sides which are more affected by the wind. In A. aspera there occur two vascular bundles in the pith with soft bast on their outer side and placed in the plane in which stone-cell groups form composite strands.
Soft bast forms groups on the outer side of xylem bundles in both the species of Aerua, while in A. aspera and P. lappacea it forms a continuous ring.
Pith consists of thick-walled cells in species of Aerua; in A. aspera and P. lappacea it is formed of large thin-walled cells.
The rhizomatous axis of A. tomentosa presents many anamolous structures. Wood forms a composite ring and is composed of a few xylem bundles with very large vessels. Medullary rays are unusually very broad ; the broadest ones broaden outwards in the form of wedges and come into contact with the cork tissue. In addition to the outer wood-ring there is a central wood cylinder developed in the pith tissue. It is composed of four diagonally placed xylem bundles, two being ​very large and with vessels large and many and the other two small with vessels small and few. Soft bast forms groups on the outer side of xylem bundles.
The central wood cylinder occupies nearly the whole of the pith. It is, I should say, secondarily developed when the axis took to a rhizomatous habit of growth ; it affords mechanical support against longitudinal pressure. In a rhizomatous axis the mecha- nical tissue, when necessary as a protection against longitudinal pressure cannofe develop in any other form than in the form of a central cylinder. This is analogous to what is seen in the case of roots. Abundance of very large vessels is necessary on account of greater abundance of moisture in the soil than in the dry air outside. This affords an example of the great plasticity of plant structures which can admirably adapt themselves to changes in their sur- roundings.
Another anamolous structure is presented in the form of groups of water-storing tracheids in the middle of the cork-tissue, with clustered crystals in their neighbourhood. The occurrence of water- storing tracheids in the cork tissue can be accounted for by the abundance of lenticels.
The fact that the conjunctive tissue of medullary rays comes into direct contact with the cork tissue at certain spots where the medul- lary rays are very broad may be accounted for as means of bringing the lenticel tissue into direct contact with the water conducting tissue and thus increasing transpiration, as there may be abundance of water in the rhizomatous axis with numerous large vessels and with numerous water-storing tracheids.
The occurrence of vascular bundles in the pith of A. aspera forms an anamolous structure. They may be necessary for supplying the extensive thin-walled pith tissue with water and also for strengthening the same against the winds of the desert, as they are developed in a plane which corresponds with the direction of the prevailing wind.
General Review. — Epidermis consists of tabular cells with outer and inner walls thickened and convexly arched outwards and inwards respectively. Stomata are accompanied by ordinary epidermal cells. Hairy covering consists of candelabra hairs or of uniseriate trichomes, with walls smooth or muriculate. Collenchyma is developed at the angles. The pericycle consists of groups of stone-cells. Wood is composite. Medullary rays are absent except in the rhizomatous axis of A. tomentosa. The pith consists of thick-walled or of thin- walled cells. Some of the members present many anamolous struc- tures which prove the remarkable plasticity of their tissues. ​
CHENOPODIACEAE.
Haloxylon recurvum Bunge. — Figs. 285, 286. Leaves semi- terate. Epidermal cells with outer walls papillose. Stomata de- pressed. Aqueous tissue subepidermal and central. Palisade tissue continuous on the upper surface and broken by aqueous cells on the lower. A bundle-sheath like layer below palisade tissue and bringing into contact the assimilatory and vascular system. Veins peripheral and central and surrounded by small-celled parenchyma. Oxalate of lime in the form clustered crystals in the subepidermal and central aqueous tissue. T. S. of the axis circular. Assimilatory tissue in the axis of palisade cells. Pericycle of thin groups of stone- cells. Peripheral bundles traversing the central aqueous tissue and the central bundles embedded in interfascicular wood prosenchyma. Pith of thick-walled cells.
Haloxylon salicornicum Bunge.— Fig. 288. Epidermis of thin-walled tabular cells. Stomata depressed. Aqueous tissue subepi- dermal and central. Palisade cells forming a continuous ring. Cluster- ed crystals in the form of a layer in subepidermal aqueous cells and also scattered in the central aqueous tissue of the leaf and axis. Bundle-sheath-like layer below palisade tissue and bringing into contact assimilatory and vascular tissues. Pericycle of stone-cell groups and isobilateral. Peripheral vascular bundles traversing the central aqueous tissue and the central vascular bundles embedded in interfascicular wood prosenchyma. Pith of thin-walled cells.
(To be continued) ​
Plate XXV.
244. Solarium incanum. T. S- of the axis.
Oc. 6 Com. ; Ob. 8 mm. Ap.
245. Anticharis linearis. T. S. of the axis.
Oc. 4 Com. ; Ob. 8 mm. Ap. 246-247. Schweinfurthia sphaero car pa.
246. T. S. of the leaf showing epidermis and hairs.
Oc. 4 Com. ; Ob. 3 mm. Ap.
247. T. S. of the axis.
Oc. 6 Com. ; Ob. 8 mm. Ap. 248-250. Blepharis sindica.
248. T. S. of the leaf showing epidermis and a stoma.
Oc. 6 Com. ; Ob. 3 mm. Ap.
249. Hair on the leaf.
Oc. 6 Com. ; Ob. 3 mm. Ap,
250. T. S. of the axis.
Oc. 6 Com ; Ob. 8 mm- Ap. 251- Ruellia patida- T- S. of the axis. Oc 6 Com- ; Ob- 8 mm. Ap.
252-257. Barleria hochstetteri.
252. T. S. of the leaf showing cystolith-like structures in epidermal cells-
Oc- 6 Com. ; Ob 8 mm- Ap.
253. Glandular hair on the leaf. Oc. 6 Com. ; Ob. 8 mm. Ap.
254- T- S- of the leaf showing a hair. Oc 6 Com. ; Ob. 8 mm. Ap. 255. T- S- of the axis showing hairs and cystolith-like structures in epidermal cells* Oc- 6 Com- J Ob. S mm. Ap-
~k- I Hair on the axis.
Oc. 4 Com. ; Ob. 8 mm. Ap-
258-259- Justicia simplex. 258. T- S- of the leaf.
Oc- 6 Com. ; Ob- 8 mm. Ap- 259- T. S. of the axis.
Oc- 4 Com. ; Ob. 8 mm. Ap.
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Plate XXVI.
260-262. Bouchea marrubifolia.
260. T. S. of the leaf showing a stoma.
Oc. 4 Com. ; Ob. 3 mm. Ap.
261. T. S. of the axis showing epidermis and hairs.
Oc. 4 Com. ; Ob. 3 mm. Ap.
262. Glandular hair on the axis. Oc. 6 Com. ; Ob. 3 mm. Ap.
263-264. Cleredsndron Phlomiciis.
263. Hair on the axis.
Oc 8 Com. ; Ob. 3 mm. Ap.
264. Glandular hair on the leaf. Oc. 6 Com. ; Ob. 3 mm. Ap.
265-267. Salvia aegyptiaca.
265. Glandular hair on the leaf. Oc. 6 Com. : Ob. 3 mm. Ap.
266. Hair on the leaf.
Oc. 6 Com. ; Ob. 8 mm. Ap.
267. T. S. of the axis.
Oc. 6 Com. ; Ob. 8 mm. Ap. 268-269. Boerhmvia diffusa.
268. Glandular hair on the leaf. Oc. 6 Com. ; Ob. 8 mm. Ap.
269. T. S. of the axis.
Oc. 6 Com. ; Ob. 8 mm. Ap. 270. Boerhaavia elegans.
T. S. of the axis showing epi- dermis. Oc. 6 Com.; Ob. 8 mm. Ap.
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Plate XXVII.
271-274. Aerua tomentosa.
271. T. S. of the axis. Oc. 3 ; Ob. C.
272. Hair on the axis. Oc. 3 ; Ob. C.
273. T. S. of the leaf. Oc. 1 ; Ob. 8 mm. Ap.
274. Stoma on the leaf. Oc. 3 ; Ob. 3 mm. Ap.
275-281. Aerua pseudo-tomentosa. lib. Stoma on the leaf. Oc. 3 ; Ob. 3 mm. Ap. 277. Hair on the leaf. Oc. 1 ; Ob. 8 mm. Ap.
280. Young hair on the axis, Oc. 3 ; Ob. C.
281. T. S. of the axis. Oc. 3 ; Ob. C.
282-284. Achyranthes aspera.
282. Hair on the axis. Oc. 1 ; Ob. 3 mm. Ap.
283. Glandular hair on the axis. Oc. 1 ; Ob. 3 mm. Ap.
284. T. S. of the axis. Oc. 2 ; Ob. C.
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Plate XXVIII
276-279. Pupalia lappacea.
276. T S. of the axis showing epidermis and collenchma. Oc. 4 Com. ; Ob. 3 mm, Ap.
278. T. S. of the ads. Oc. 2 ; Ob. G.
279. Hair on the axis. Oc. 2 ; Ob. C.
285-286. Haloxylonrecurvam. 285. T. S. of the lear.
Oc. 2 Com. ; Ob. 8 mm. Ap. 286. T. S. of the axis. Oc. 2 Com. ; Ob. 8 mm. Ap.
287. Salsolafoettda. Hair on the axis.
Oc. 4 Com.; Ob. 3 mm. Ap.
288. Haloxylon salicornicum. T. S. of the axis.
Oc. 2 Com. ; Ob. 8. mm. Ap.
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