PLANTS OP THE INDIAN DESEKT. 283 



are thickened in Capparidaceac and Euphorbiaceae, angular in Cyper- 

 aceae and gelatinised in Violaceae, Rhamneae and Sapindaceae. The 

 thickening of inner walls reduces the loss of water. Mucilaginous 

 modifications of the inner walls have the property of absorbing and 

 retaining water ; and the epidermis, thus, forms a water-storing 

 tissue. The epidermal cells in the Cy per aceae, which form an 

 articulation tissue, have inner-walls angular, so that they come into 

 close contact with the inner cells of the articulation tissue. 



The articulation tissue is of epidermal origin and is extensively 

 developed in Cy per aceae and Gramineae. It usually forms strands of 

 fchin-walled cells running between two surfaces of the leaf. In the 

 Cyperaceae it forms usually a many-layered tissue in the upper half 

 of the leaf. The margins curve upwards as on a hinge and protect 

 sfcomata on the upper surface of the leaf in Gramineae as well as 

 watery contents in the aqueous cells of the articulation tissue in 

 both the orders. 



The epidermis in Violaceae, Celastraceae and Gramineae is char- 

 acterised by palisade-like elongation of epidermal cells. Large cells, 

 intercalated among ordinary epidermal cells, distinguish Cappari- 

 daceac, Elatineae, Malvaceae, Moring aceae, Lcguminosae, Ficoideae, 

 Salvadoraceae and Polygonaceae. Both of these characters are con- 

 trivances for storage of water. 



The epidermis is sometimes locally two-layered by means of 

 cross walls parallel to the surface, appearing in the epidermal cells of 

 Violaceae, Tamariscineae, Burseraceae, Celastraceae, and Salvadoraceae. 

 In Violaceae and Burseraceae the inner walls are gelatinised and a 

 mucilaginous mass is found beneath the division walls. It is usually 

 two-layered in the axis of some of the species of Polygalaceae, Elatineae, 

 Geraniaceae, Papilionaceae, Salvadoraceae, Asclepiadaceae and Euphor- 

 biaceae. The occurrence of a two- layered epidermis either locally or 

 throughout intensifies the protective function of the epidermis, name- 

 ly that of reducing the loss of water by transpiration. 



Yellowish contents in the epidermal cells of Rhamneae are of the 

 nature of cellulose slime which reduces loss of water by transpiration 

 by thickening the watery contents in the cells. Cystolith-like struc- 

 tures occur in the basal cells of clothing hairs of Cucurbitaceae and 

 Boraginaceae and also in large cells intercalated amongst ordinary 

 epidermal cells in Acauthaceae. Calcareous cystolith-like structures 

 give an acrid taste to juices of foliage and prevent the plants from 

 being easily devoured by animals. The epidermis, in Actinioptcris 

 dichotoma which is the only Eern found in the Indian Desert, is 

 mostly sclerosed. This sort of modification of the epidermis is 



