The Journal of Indian Botany/Volume 2/May 1921/The Physiological Anatomy of the Plants of the Indian Desert
THE Journal of Indian Botanp* Vol. II. MAY, 1921. No. 3.
THE PHYSIOLOGICAL ANATOMY OF THE PLANTS OF THE INDIAN DESERT BY T. S. Sabnis, B.A., M.Sc, St. Xavier's College, Bombay. N! V YORK 'AKiCAL {Continued from p. 13.) o-WI>FN
BORAGINACEAE
Ehretia aspera B.— Figs. 202, 203. Woody. Mesophyll isobi- lateral. Veins provided with bundle-sheath. Tanniniferous secretions in the sheath cells and in cells of the middle tissue. Hairs unicellular and with verrucose walls. Pericycle of large groups of stone-cells. Bast fibres in soft bast. Pith of cells with lignified walls. Solitary crystals in some of the pith cells.
Heliotropium supinum L. — Fig. 204. Herbaceous. Mesophyll of palisade tissue on the upper side and of arm-palisade tissue on the lower. Veins provided with bundle-sheaths. Hairs unicellular and with verrucose walls. Middle tissue absent. Pericycle of groups of bast fibres. Pith of thin-walled cells.
Heliotropium rariflorum Stks.— Pigs. 205, 206, 207, 208, 209, 211. Woody. Mesophyll isobilateral- Veins provided with bundle-sheaths. Bundle-sheath cells and cells of the middle tissue with tanniniferous contents. Pericycle of groups of stone-cells. Pith of cells with lignified walls. Some of the pith cells with solitary crystals.
Heliotropium undulatum Woodr. — Pigs. 212, 213, 214 Woody. Mesophyll isobilateral. Middle tissue present. Clustered crystals in the mesophyll. Trichomes with terminal cell curved and with verrucose walls. Pericycle of groups of stone-cells. Pith of thin-walled cells.
Heliotropium paniculatura L— Figs. 215, 216. Woody. Meso- phyll formed of palisade tissue on the upper side and of arm-palisade tissue on the lower. Middle tissue present. Hairs unicellular and with verrucose walls. A layer of colourless tabular cells on the inner side of the assimilatory tissue in the axis. Endodermis with granular contents. Pericycle formed of groups of stone-cells. Pith of thin-walled cells with granular contents.
Tricodesma indicum Br. — Figs. 217, 218. Quite herbaceous. Mesopbyll formed of palisade tissue on the upper side and of arm-palisade tissue on the lower. Veins with bundle-sbeaths. Middle tissue absent. Sclerenchymatous pericycle not developed. Pith of thin-walled cells.
Sericostoma pauciflorura Sths. — Figs. 219, 220. Woody. Mesophyll isobilateral. Middle tissue present. Hairs unicellular and with verrucose walls. Pericycle forming a composite ring of stone-cells. A layer of colourless tabular cells on the inner side of the assimilatory tissue in the axis. Pith of thin-walled cells.
Arnebia hispidissima DC. — Figs. 221, 222, 223. Herbaceous. Mesophyll formed of palisade tissue on the upper side and of arm-palisade tissue on the lower. Middle tissue absent. Veins with bundle-sheaths. Hairs unicellular and with verrucose walls. Pericycle formed of isolated stone-cells. Pith of cells with lignified walls.
Structure of the Leaf. — The epidermal cells have the outer walls greatly thickened. The inner walls are thin and more or less undulated. The outer walls are muriculate in E. aspcra and A. hispidissima ; they are convexly arched outwards inT. indicum and S. puvci- florum. Some of the epidermal cells in H, rariflorum and T. indicum are vertically elongated, while the rest are tabular or polygonal ; this peculiarity in shape may be supposed to mark the commencement of unicellular hairs (fig. 206.) These hairs have been observed at different stages of development (fig. 206, 207, 208). It seems that the epidermal cells at these spots divide by vertical walls ; the daughter cells then elongate and present a shape as in (figs. 210, 217). One of these daughter cells then elongates still more and gives rise to a small unicellular hair with a large lumen and with a broad base. These hairs will be discussed in greater detail under the hairy covering. The stomata are usually placed in depressions produced either by the thickened or papillose outer epidermal cells. The guard-cells are in the plane of the surrounding cells. The stomata are more numerous in members with a larger number of veins. In H. paniculatum there is a sort of depression produced by the downwardly projecting mid-rib and by the downwardly curved margins. In this portion stomata as well as hair-like epidermal cells are more numerous than on the upper surface. The stomata are thus protected from direct sun light and transpiration is very much checked.
The mesophyll is isobilateral in E. aspera, 3. rariflorum, H. undulatum and S. pauciflorum ; in E. aspera palisade cells on the upper side are much longer than those on the lower. It consists of palisade tissue on the upper side and of arm-palisade tissue on the lower in H. supinum, H. panicidatum, T. indicum and A. hispidissima. There is a tissue of large thin-walled colourless polygonal cells in the middle of the mesophyll of all members except H. supinum, T. indicum and A. hispidissima. This tissue, which may be termed the middle tissue, seems to partake in the formation of bundle-sheaths. The cells of the middle tissue may hold clustered crystals, or tanniniferous contents, or they may serve occassionally as water-reservoirs.
Internal secretory organs are represented by tannin sacs confined to the middle tissue of the mesophyll, or to the bundle-sheaths. The cells of the middle tissue as well as those of the bundle-sheaths in H. rariflorum and E. aspera hold tanniniferous contents which are confined only to the sheath-cells, or to the cells of the middle tissue in II. panicidatum and H. undulatum respectively.
Oxalate of lime is present in the form of clustered crystals in groups of cells between the middle tissue and epidermis on either side in 3. undulatum (fig. 212). Solitary crystals are found in the pith cells of E. aspera and 3. rariflorum.
Calcium carbonate is deposited either in the outer epidermal walls as in 3. supinum or in walls of clothing hairs as in other members. Deposits of calcium carbonate give a warty appearance to the surface of the leaf or to the walls of the hairs, and they are the cause of roughness of the leaf and of the axis.
The veins are embedded in all members except in E. aspera in which they are vertically transcurrent above and below by sclerenchyma. Bundle-sheaths occur round the veins in E. aspera, 3. supinum, 3. rariflorum, T. indicum and A. hispidissima. The veins of the mid-rib are protected by thin-walled collenchyma which surrounds them. The vascular bundles are bicollateral in 3. panicidatum. The veins are numerous in all members except in herbaceous members, viz : 3- supinum, T. indicum and A. hispidissima- They anastomose freely and are prominent either on both the surfaces as in 3. rariflorum or only on the lower surface as in E. aspera and 3. undulatum- The veins of the mid-rib are prominent on the lower side in all the members. Upper surface of the mid-rib is grooved in S. pauciflorum. The scantiness of the veins is characteristic of leaves of herbaceous members, while their abundance and anastomosis distinguish the leaves of woody members. Though the veins are numerous in the latter, transpiration is arrested by the thickened and cuticularised outer epidermal walls, by the poorly developed ventilating system and by the abundance of tannin in cells of the mesophyll.
The clothing hairs on the leaf and axis in all members except H. supinum are characterised by calcification of their walls which are consequently verrucose and rough. Some of the epidermal cells In these members undergo a division by vertical walls as in (fig. 210) and elongate as shown in (figs. 207, 208, 209). The walls of the terminal portion are secondarily impregnated with calcium carbonate. The hairs thus formed are unicellular, conical and have a broad thin-walled base. They are found in the leaf and axis of all members except H. supinum. Besides these, there are found other forms of clothing hairs in the different members. In E. aspera (fig. 202), T. indicum (fig. 218) and A. hispidissima (figs. 221, 222, 223) are found unicellular hairs which have a thin-walled bulbous base and a tapering terminal portion with walls, verrucose or smooth as in H. supinum. Hairs in H. undulatum consist of a thin- walled basal cell and of a long appressed terminal cell with verrucose walls. Cystolith-like structures occur in the basal portions of the hairs of S. pauciflorum, A. hispidissima, H. rariflorum and H. undulatum, T. indicum.
It should be observed in all these forms of hairs that the basal portion is bulbous and thin-walled and it may be a means of absorbing water trickling down the terminal portion. Hairs, when not numerous, are more or less appressed as in E. aspera and H. undulatum and they form a suitable light screen.
Glandular hairs are not common. They are found in a very small number in H. supinum, and they consist of a stalk-cell and of a spherical unicellular head.
Structure of the Axis : — The epidermal cells have outer walls thickened and cuticularised in all members except the herbaceous ones. The lateral walls are usually thin and undulated. Some of the epidermal cells in T. indicum and S. pauciflorum are large and vertically elongated (figs. 217, 220); and give rise to a somewhat ribbed appearance to the axis. These cells may have the function of giving rigidity to the epidermal tissue. The primary cortex is generally characterised by an assimilatory tissue which consists either of palisade cells as in H. undulatum (fig. 214), or of arm-palisade tissue as
in S. pauciflorum (fig. 220) and A. hispidissima, or of chlorenchyma as in E. Aspera, H. supinum, H. panic ulatum (fig. 216) and T. indicum. There is a two-layered tissue of large thin-walled, colourless tabular | A table should appear at this position in the text. See Help:Table for formatting instructions. |
may ba of the nature of secretory cells. Cork is well developed and is subepidermal in E. aspera. The endodermis is not differentiated except in H. panic id at um in which it is characterised by granular contents.
The pericycle forms a composite ring of stone-cells in S. pauci- florum ; it is composed of closely placed groups of stone-cells in E. aspera, H. rariflorum, H. panicxdatum and H. undUlatum. It consists of isolated stone-cells in A. hispidissima and of groups of bast fibres in H. supinum. A sclerenchymatous pericycle is not developed in T. indicum, which is quite herbaceous. There are large groups of bast fibres in the soft bast of E. aspera.
The wood forms a composite ring in all members. The perfora- tions of the vessels are simple. It should be observed that in herbaceous members vessels are large and numerous in correspondence with more vigorous transpiration. The development of interfascicular wood prosenohyma is in inverse proportion to the size and abundance of the vessels. The abundance of medullary rays usually corresponds with that of vessels. Some of the vessels towards the pith are found to hold tanniniferous contents. The pith consists of small cells with lignified walls in E. aspera, H. rariflorum and A. hispidissima ; in other members it is formed of very thin- walled cells. The pith cells of II. panicidatum hold granular contents. The pith is strengthened by sieve-sclereids in H. rariflorum (fig. 211 SVJ.
CONVOLVULACEAE.
Cressa cretica L.— Figs. 224, 225. Guard-cells in the same plane. Front cavity in depression produced by outer thickened epidermal walls. Mesophyll isobilateral. Internal secretory organs and oxalate of lime absent. Veins provided with green bundle-sheaths. Clothing hairs two-armed. Glandular hairs horizontal. Pericycle formed of closely placed groups of stone-cells. Assimilatory tissue in the axis formed of palisade cells. Wood composite. Pith of thin-walled cells.
Breweria latifolia Bth. — Figs. 226, 227. Guard-cells on the same plane. Front cavity placed in depression formed by outer thickened epidermal walls. Mesophyll isobilateral. Internal glands in the form of colourless secretory cells surrounded by specialised subsidiary cells in the mesophyll. Clustered crystals near veins, in cortex and pith. Solitary crystals in outer soft bast. Veins provided with green bundle-sheaths. Larger veins vertically transcurrent. Clothing hairs two-armed. Glandular hairs absent. Fericycle formed of isolated stone-cells and of very small stone-cell groups. Assimilatory tissue in the axis formed of chlorenchyma. Wood composite. Pith of thick- walled cells.
Convolvulus microphyllus Sieb — Figs. 228, 229. Guard-cells elevated. Front cavity placed in a depression formed by outer thickened epidermal walls. Mesophyll isobilateral. Veins embedded and provided with green bundle-sheaths. Internal glands and oxalate of lime absent. Terminal cell of the clothing hairs seated obliquely on the stalk cell. External glands spherical on the leaf and club- shaped on the axis. Pericycle formed of thin long groups of stone-cells. Aasimilatory tissue in the axis formed of palisade cells. Wood composite and narrowed on two opposite sides. Pith of thin-walled cells.
Convolvulus glomeratUS Chois.— Fig. 230. Guard-cells ele- vated. Front cavity on a level with the surface. Mesophyll of palisade tissue on the adaxial side and of arm-palisade tissue on the abaxial side. Secretory cells with surrounding subsidiary cells present. Oxalate of lime absent. Veins embedded and without bundle-sheaths. Clothing hairs with terminal cell vertically placed on the stalk cell. External glands club shaped. Assimilatory tissue in the axis parenchymatous. Pericycle of closely placed thin long groups of stone-cells. Wood composite and narrowed on two opposite sides. Pith of thin- walled cells.
Ipomoea sindica Stapf.— Figs. 231, 232, 233, 234, 235. Guard- cells elevated. Front cavity on a level with the surface. Mesophyll of palisade tissue on the adaxial side and of arm-palisade tissue on the abaxial side. Internal glands absent in the leaf and found in the axis in the form of secretory cells with tanniniferous contents. Oxalate of lime absent. Terminal cell of clothing hairs superficially knobbed and seated vertically on the stalk-cell which is placed on an epidermal cell in the leaf and on a multicellular pedestal on the axis. External glands horizontal. Assimilatory tissue in the axis parenchymatous. Wood composite and narrowed on two opposite sides. Pericycle forming a composite ring of stone-cells. Pith of thin-walled cells with granular contents.
Structure of the Leaf: — The epidermis consists of tabular cells with the outer walls thickened and convexly arched outwards ; inner walls are also thickened. The lateral walls are thin and straight. The cuticle is thin and striated.
The stomata are developed equally on both the surfaces of isobilateral leaves ; they are more numerous on the lower surface of bifacial leaves of C. glomeratus and /. sindica. Guard-cells are elevated in C. microphyllus (tig. 228), G. glomeratus and I- sindica (figs. 231, 232); they are placed in the plane of surrounding cells in other members. The guard-cells are accompanied by subsidiary cells except in C. cretica. The front cavity is on a level with the surface in C. glomeratus and I. sindica (fig. 233) ; in other members it is placed in a depression formed by thickened outer epidermal walls. The elevated position of the guard-cells may be due to the occurrence of a dense protective covering of clothing hairs.
The mesophyll is isobilateral (fig. 228) in all members except C. glomeratus and I. sindica (fig. 231), in which it consists of palisade tissue on the adaxial side and of arm-palisade tissue on the abaxial side.
Internal secretory organs occur in the form of secretory cells in the middle of the mesophyll of B. kitifolia and C. glomeratus and in cortex and pith of I. sindica (fig. 234 G). In B. latifolia and G. glomeratus they consist of colourless secretory cells with surrounding arm-palisade cells differentiated into subsidiary cells. Secretory cells in /. sindica are greatly horizontally elongated and hold tanniniferous contents.
Oxalate of lime occurs in the form of clustered crystals in the neighbourhood of veins and in the cortex and pith, and in the form of solitary crystals in the soft bast of B. latifolia. In other members oxalate of lime is not found.
The veins are embedded except some of the larger ones in B. latifolia which are vertically transcurrent above and below by collen. chyma. The veins in G. cretica, B. latifolia and G. microphallus (fig. 228) are provided with green bundle-sheaths. Vascular bundles of the veins are bicollateral.
Hairy covering consists of clothing and glandular hairs. Clothing hairs are composed of a terminal cell of variable shape and of a stalk-cell seated either upon a single epidermal cell, or on two epidermal cells formed by a vertical wall (fig. 231), or on a multicellular pedestal of epidermal cells (fig 235).
The terminal cell is simple and is seated straight upon the stalk-cell in C. glomeratus (fig. 230) or seated obliquely on the stalk-cell in C, microphyllus (fig. 228). In 1. sindica the stalk-cell of clothing hairs on the leaf is placed vertically on a single epidermal cell or on two epidermal cells formed by a vertical division wall (fig. 231) ; the stalk-cell on the axis is seated vertically on a multicellular pedestal of epidermal cells (fig. 235). The terminal cell bears minute solid knobs on the surface.
In G. cretica (figs. 224, 225) and B. latifolia (fig. 226), the terminal cell is two-armed ; arms are of uniequal length and are horizontally placed. The stalk-cell is cylindrical. On the axis of C. microphyllus there are large cells, bearing clothing hairs intercalated amongst epidermal cells of ordinary dimensions.
The glandular hairs are placed in epidermal depressions and consist of an unicellular stalk-cell seated upon an epidermal cell which is much depressed and of a head. The head is either club-shaped and divided by horizontal walls as in. G. cretica (fig. 224) and G. glomeratus, or spherical and divided both by horizontal and vertical walls as in C. microphyllus (fig. 228), or flat and divided by horizontal walls as in T. sindica (fig. 231)
The lower cells of the head of club-shaped glands are also vertically divided (fig. 224). The walls of external glands with spherical heads are very thin. External glands seem to be absent in. B. latifolia.
Clothing hairs as well as external glands are less numerous on the axis than on the leaf. This is due to the expanded surface of the latter which is more exposed to direct rays of the sun.
Structure of the Axis. — The epidermis consists of tabular cells with outer and inner walls thickened and convexly arched outwards and inwards respectively. The lateral walls undulated in C. cretica and G. glomeratus. In G. microphyllus large pyramidal cells are inter- calated amongst epidermal cells of ordinary dimensions and usually bear clothing hairs. The cuticle is striated. The primary cortex is characterised by the presence of assiruilatory tissue formed either of palisade cells as in G. cretica (fig. 225) and C. microphyllus (fig. 229) or of chlorenchyma as in other members (fig. 234).
The pericycle in G. cretica and in both the species of Convolvulus is composed of closely placed long thin groups of stone-cells ; in I. sindica it forms a composite ring of stone-cells. In B. latifolia the pericycle consists partly of isolated stone-cells and partly of very small stone-cell groups. It undergoes reduction on a small portion of the lower side of the inclined axis of C. cretica, where it consists of a few isolated stone-cells. A well developed sclerenchymatous pericycle is necessary on the upper side of the inclined axis to prevent the axis from bending.
The wood is composite. The vessels have simple perforations and the medullary rays are uniseriate. The vessels are numerous and are arranged in rows in G. cretica (fig. 225), C. glomeratus and I. sindica (fig. 234) ; in other members the vessels are few. The abun- dance of interfascicular wood prosenchyma is inversely proportional to that of vessels.
In both the species of Convolvulus and in /. sindica small portions on diametrically opposite sides of the wood-ring are much narrowed 1239—10 and possess a few small vessels. The wood-ring in G, cretica is much narrowed on one side where there are a few small vessels.
These modifications in the structure of wood may be due to the influence of the direction of the prevailing wind in the first case, and to the inclined position of the axis in the second case. The reduction of wood, accompanied also by reduction of the sclerenchymatous pericycle in G. cretica,, takes place on those sides of the axis which are less affected by the prevailing wind and on the lower side of the inclined axis which is less exposed to the sun and wind and possess consequently less functional activity.
Vascular bundles in all members are bicollateral and there are two rings of soft-bast, one on the outer side and another on the inner side of the wood-ring.
The pith consists of thin-walled cells in all members except in B. latifolia where it consists of cells with thickened and lignified walls. The pith cells in I. sindica are mostly filled with granular contents.
General Revieiv. — The epidermal cells are not much thick-walled ; but have the outer and inner walls convexly arched outwards and inwards respectively. The guard-cells are elevated and are associated with subsidiary cells. The mesophyll is either isobilateral or is composed of palisade tissue on the upper side and of arm-palisade tissue on the lower. Internal glands, when present, consist of colourless secretory cells with surrounding subsidiary cells or of secretory cells with tanniniferous contents. Veins are embedded with the exception of some of the larger veins which are vertically transcurrent ; they may or may not be provided with bundle-sheaths. Oxalate of lime occurs in the form of clustered or solitary crystals, or it may not be found.
The clothing hairs are composed of a stalk-cell, seated upon a single epidermal cell or on a pedestal and of a terminal cell which may be simple and placed vertically or obliquely on the stalk-cell, or which may be two-armed. External glands are placed in epidermal depressions and are composed of a stalk-cell and of a head which may be club-shaped, spherical or horizontal. The head may be divided only by horizontal or vertical walls or by both.
The assimilatory tissue in the axis is composed of palisade cells or of chlorenchyma. The pericycle either forms a composite ring of stone-cells, or is formed either of large groups of stone-cells or of isolated stone-cells. Vascular bundles are bicollateral and the wood is composite. Interfascicular wood prosenchyma is not abundant and medullary rays are uniseriate. The wood as well as the pericycle undergo modifications due to differences in functional activity in different portions of the axis which are not equally affected by the sun and wind. The pith consists of thin-walled cells or of cells with thickened and lignified walls.
SOLANAGEAE.
Solanum incanum L. — Figs. 241, 242, 243, 244. Mesophyll bifacial. Oxalate of lime found in the form of crystal sand in mesophyll, cortex, soft-bast, intraxylary phloem and pith. Clothing hairs tufted. Epidermis one layered. Cork subepidermal. Collenchyma developed below cork. Pericycle forming a loose ring of bast fibres. Vessels arranged in bundles connected by strands of interfascicular wood prosenchyma.
Solanum albicaule Kotsc — Figs. 236, 237, 238. Mesophyll isobilateral. Oxalate of lime found in the form of crystal sand in mesophyll and pith. Clothing hairs tufted and uniseriate trichomes. Epidermis of the axis three layered. Collenchyma subepidermal. Vessels few and uniformly distributed in the wood-ring. Intraxylary phloem present.
Lycium barbarum L.— Fig. 239. Mesophyll isobilateral. Oxal- ate of lime found in the form of crystal sand in mesophyll of the leaf and epidermis s soft bast and pith of the axis. Clothing hairs absent. Epidermis of the axis one-layered and with outer walls thickened and muriculate. Sclerenchymatous pericycle not developed. Cork subepidermal and characterised by isolated stone-cells. Vessels few and uniformly distributed in the wood-ring. Intraxylary phloem present-
Structure of the Leaf : — The epidermal cells are tabular with the outer walls thickened and convexly arched outwards. The lateral walls are thin and undulated. The outer walls in L. barbarum (fig. 239) are muriculate. The upper epidermal cells are mostly filled with crystal sand.
The stomata are equally numerous on both the surfaces of isobi- lateral leaves, while they are more numerous on the lower surface of bifacial leaves. The front cavity is placed in a depression formed by outer thickened epidermal walls. The guard-cells are accompanied by ordinary epidermal cells.
The mesophyll is isobilateral in S. albicaule and L. barbarum and is bifacial in S. incanum. Some of the palisade cells contain crystal sand.
Oxalate of lime occurs in the form of crystal sand in all members. Cells filled with crystal sand are found abundantly in the mesophyll of the leaf and in the epidermis of the axis of L. barbarum , Cells with crystal sand occur in medullary rays and outer soft bast of S. incanum and L. barbarian. Crystal sand occurs abundantly in cortex and inner soft bast of S. incanum. The abundance of oxalate of lime in the leaf and axis gives an acrid taste to the tissues of the plants and prevents them from being easily devoured by animals.
Veins are embedded and are not provided with bundle-sheaths.
The hairy covering consists of clothing and glandular hairs. The clothing hairs on the leaf and axis of both the species of Solatium are tufted. They consist, in S. albicaule, of a short biseriate stalk and of a tuft'of ray-cells, some of the rays being uniseriate (fig. 236). In S. incanum (fig. 242), the stalk is multiseriate and is usually longer on the axis. In addition to the tufted hairs in <S. albicaule, there are uniseriate trichomes (fig. 238). Clothing hairs are absent in L. barbarum.
Glandular hairs occur in leaf and axis of L. barbarian and of both the species of Solanum ; and are composed of a short uniseriate stalk and of an ellipsoidal head which is irregularly divided (fig. 237).
Structure of the Axis. — The epidermis consists of a single layer of tabular cells with the outer walls greatly thickened and convexly arched outwards in S. incanum and L- barbarian. The epidermis in S. albicaule is composed of more than one layer (three layers in the specimen examined) of vertically tabular cells which are uniformly thickened a little on all sides. The epidermal cells of L. barbarian are mostly filled with crystal sand. The cortex in S. incanum, and L. barbarian is characterised by cork which is subepidermal. Cork in L. barbarian is strengthened by isolated stone-cells. The collen- chyma is subepidermal as in S. albicaule, or it occurs below the cork as in other members. In <S. incanum collenchyma is extensive and the inner portion of the cortex consist of large polygonal cells, some of which are filled with crystal sand.
The pericycle forms a loose ring of bast fibres in both the species of Solanuvi. Scleranchymatous pericycle is '■ not developed in L. barbarian.
The wood is composite in all members. Medullary rays are uniseriate and numerous. The vessels are few and large and are uniformly distributed in rows in the wood ring of S. albicaule and L. barbarian ; interfascicular wood prosenchyma is extensive and consists of cells with thickened walls and with small lumen. In S. incanum the vessels are large and are arranged in bundles which are connected by strands of interfascicular wood prosenchyma, formed of cells with thin walls and large lumen. The wood-ring in S. incanum is narrowed in a small portion on one side where it con- sists of a few vessels and of extensive connecting strands of interfascicular wood-prosenchyma. This narrowed portion of the wood-ring represent the lower side of the inclined axis where the functional activity is comparatively much less. In addition to the normal zona of soft bast on the outer side of the wood-ring there are groups of intraxilary soft bast on its inner side. Intraxilary soft bast is protected on its inner side by groups stone-cells. The pith consists of thin-walled cells. Some of the pith cells contain crystal sand.
General Review : — The epidermal cells have their outer walls greatly thickened and cuticularised. The stomata are depressed and occur on both the surfaces ; they are surrounded by ordinary opidermal cells. The mesophyll is bifacial or is isobilateral. Oxalate of limo occurs abundantly in the form of crystal sand in the leaf and axis. The clothing hairs usually consist of a biseriate or multiseriate stalk and of a tuft of ray cells. In addition to the tufted hairs, uniseriate trichomes are found in S. albicaule. Glandular hairs are composed of a short uniseriate stalk and of an ellipsoidal head which is irregularly divided. The epidermis of the axis is one-layered or many-layered. The cork is sub-epidermal. The sclerenchymatous pericycle, when present, forms a loose ring of bast fibres. All the members are characterised by the occurrence of intraxilary soft bast. The vessels have simple perforations. The interfascicular wood prosenchyma is extensive. The medullary rays are uniseriate and numerous. Wood parenchyma is little developed. Pith consists of thin- walled cells.
(To be continued.) Plate XXII.
202-203. Ehretia aspera.
202. T. S. of the leaf.
Oc. 6 Com.; Ob. 8 mm. Ap.
203. T. S. of the axis.
Oc. 4 Com.; Ob. 8 mm. Ap.
204. Heliotropium supinum.
Hair on the leaf.
Oc. 2 Com.; Ob. 3 mm, Ap.
205-211. Heliotropium rariflorum.
205. T. S. of the leaf.
Oc. 4 Com.; Ob. 8 mm. Ap.
206 207 208 209 Hair on the leaf in different stages of development.
Oc. 4 Com.; Ob. 8. mm. Ap.
210. T. S. of the leaf showing epidermis, stomata and cystolith-like structures.
Oc. 4 Com.; Ob. 8 mm. Ap.
211. T. S. of the axis.
Oc. 6 Com.; Ob. 8 mm. Ap.
212-214. Heliotropium undulatum.
212. T. S. of the leaf.
Oc. 6. Com.; Ob. 8 mm. Ap.
213. Hair on the leaf.
Oc. 8 Com.; Ob. 8 mm. Ap.
214. T. S. of the axis.
Oc. 4 Com.; Ob. 8 mm. Ap.
N.B.—To get the original dimensions multiply by 1·7. 
Plate XXIII.
215-216. Heliotropium paniculatum.
215. T. S. of the leaf.
Oc. 8 Com.; Ob. 8 mm. Ap.
216. T. S. of the axis.
Oc. 2 Com.; Ob. 3 mm. Ap.
217-218. Trichodesma indicum.
217. T. S. of the axis showing epidermis.
Oc. 6 Com.; Ob. 8 mm Ap.
218. Hair on the axis.
Oc. 2 Com.; Ob. 8 mm. Ap.
219-220. Sericostoma pauciflorum.
219. T. S. of the leaf.
Oc. 6 Com.; Ob. 8 mm. Ap.
220. T. S. of the axis showing epidermis, assimilatory tissue and cortical parenchyma.
Oc. 4 Com.; Ob. 8 mm. Ap.
221-223. Arnebia hispidissima.
221. 222. Hair on the leaf.
Oc. 8 Com.; Ob 8 mm. Ap.
223. Hair on the axis.
Oc. 2 Com.; Ob. 8 mm. Ap.
224-225. Cressa cretica.
224. T. S. of the leaf showing epidermis and hairs.
Oc 4 Com.; Ob. 8 mm. Ap.
225. T. S. of the axis.
Oc. 6 Com.; Ob. 8 mm. Ap.
226-227. Breweria latifolia.
226. Hair on the leaf.
Oc. 4 Com.; Ob. 3 mm. Ap.
227. T. S. of the axis showing a lenticel.
Oc. 6 Com.; Ob. 8 mm. Ap.
228-229. Convolvulus microphyllus.
228. T. S. of the leaf.
Oc. 4 Com.; Ob. 8 mm. Ap.
229. T. S. of the axis.
Oc. 6 Com.; Ob. 8 mm Ap.
230. Convolvulus glomeratus.
Hair on the axis.
Oc. 4 Com.; Ob. 8 mm. Ap.
N.B.—To get the original dimensions multiply by 1·7. 
Plate XXIV.
231-235. Ipomoca sindica.
231. T. S. of the leaf.
Oc. 6 Com.; Ob. 8 mm. Ap.
232. Hair on the leaf.
Oc. 8 Com.; Ob. 8 mm. Ap.
233. Stoma on the lower surface of the leaf.
Oc. 6 Com.; Ob. 3 mm. Ap.
234. T. S. of the axis.
Oc. 6 Com.; Ob. 8 mm. Ap.
235. Hair on the axis.
Oc. 4 Com.; Ob. 8 mm. Ap.
236-238. Solanum albicaulc.
236. Hair on the leaf.
Oc. 2 Com.; Ob. 3 mm. Ap.
237. Glandular hair on the leaf.
Oc. 4 Com.; Ob. 3 mm. Ap.
238. T. S. of the axis showing epidermis, hair and cork.
Oc. 4 Com.; Ob. 3 mm. Ap.
239-240. Lycium barbarum.
239. T. S. of the leaf showing epidermis.
Oc. 4 Com.; Ob. 3 mm. Ap.
240. T. S. of the axis showing epidermis, cortical parenchyma and cork.
Oc. 4 Com.; Ob. 3 mm. Ap.
241-243. Solanum incanum.
241. T. S. of the leaf.
Oc. 4 Com.; Ob. 3mm. Ap.
242. Hair on the leaf.
Oc. 4 Com.; Ob. 8 mm Ap.
243. Hair on the leaf.
Oc. 2 Com.; Ob. 8 mm. Ap.
N.B.—To get the original dimensions multiply by 1·7. 