282 THE JOUENAL OF INDIAN BOTANY. 



CONCLUDING REMARKS. 



Epidermis. — As a general rule, the epidermal cells on the upper 

 surface of the leaves are larger than those on the lower and epidermis 

 of the axis in the same species consists of much smaller cells than 

 those of the leaves. The epidermal cells are generally tabular with outer 

 walls convexly arched outwards. The outer walls are flat in Menisper- 

 maceae, Commelinaceae and Cyperaceae. The outer walls are thickened 

 except in Tamariscineae and Commelinaceae, the thickening being 

 considerable in Capparidaceae, Tiliaceae, Gaagraceac, Bubiaceae, 

 Gentianaceae, Scrophulariaceae, Acanthaceae, Verbcnaceae, Labiatae. 

 Amarantaceae, Polygonaceae and Euphorbiaceae. The outer walls 

 when flat are generally smooth ; when they are convexly arched, 

 outwards, as is generally the case, they are {a) either superficially 

 granulated in Portulaceae, Zygophyllaceae, Ficoideae, Asclepiadaceae 

 and Chenopodiaceae, (b) or with cuticle striated in Simarubaceae, 

 Lythraceae, Gentianaceae, Convolvulaceae, Scrophulariaceae and 

 Polygonaceae, (c) or with cuticle muriculate in Violaceae, Rubtaceae, 

 Boraginaceae and Solanaceae, {d) or with cuticle toothed in certain 

 Lcguminosae, Ficoideae, Compositae, (/) or with papillose differ- 

 entiation in Capparidaceae, Caryophyllaceae, Malvaceae, Geraniaceae, 

 Moringaceae, Caesalpinieae, Euphorbiaceae and Gramineac. 



It should be noted that in succulent plants the outer walls are 

 flat and that in other plants they undergo various modification. 

 Convexity and papillose differentiation of the outer walls are chiefly 

 useful for reflecting back the rays of light ; and in the case of papillose 

 differentiation the papillae can also retain a comparatively moist 

 atmosphere in the interspaces between them. The thickening of the 

 outer walls reduces the loss of water by way of transpiration which 

 is accelerated by various climatic factors in the desert. Cuticle, 

 roughened in various ways as described above, can absorb less light 

 and can thus reduce the loss of water which is accelerated by the 

 strong glare and sun light reflected from the sand. The hard excres- 

 cences on the surface of the leaf and axis are produced by the defi- 

 ciency of water. 



The lateral walls are either straight or undulate. The latter 

 character is common among the desert plants and givos rigidity to the 

 epidermis. 



The inner walls are usually thin and convexly arched inwards, 

 much more so in Elatineae and Geraniaceae, thus coming into close 

 contact with the assimilatory tissue. They, however, undergo various 

 modifications which are all instances of xerophytic characters. They 



