Page:The Journal of Indian Botany.djvu/489

 jecting 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.