278 THE JOUKNAL OF INDIAN BOTANY. 



The pith is composed of thin-walled cells and is characterised in 

 A. baccifera by small groups of thick-walled cells, having the same 

 size and shape as that of the pith cells. These cells form probably 

 the strengthening tissue of the pith. 



ONAGRACEAE 



Trapa bispinosa Roxb.— Fig. 127. Leaf only.— Epidermis 

 formed of tabular cells with outer walls very greatly thickened on the 

 upper surface. Stomata occurring only on the upper surface. Clothing 

 hairs in the form of uniseriate trichomes and found only on the lower 

 surface. Mesophyll formed of palisade tissue on the adaxial side and 

 of spongy tissue on the abaxial side. Spongy tissue characterised by 

 large intercellular spaces. Oxalate of lime found in the form of 

 numerous clustered crystals. Veins embedded and not provided with 

 bundle-sheaths. 



Structure of the Leaf, — The epidermal cells are tabular and 

 thin-walled on the lower surface. The outer walls of the epidermal 

 cells on the upper surface are very greatly thickened. The lateral 

 walls are straight. Stomata occur in large number only on the upper 

 surface and are surrounded by ordinary epidermal cells. Guard- 

 cells are situated in the plane of the surrounding cells and the front 

 cavity is on a level with the surface. Closure of the stomata seems 

 to take place by the well developed cuticular ridges of the guard-cells 

 (fig. 127). 



Hairy covering consists of long uniseriate thin-walled trichomes 

 occurring only on the lower surface (fig. 127). External glands are 

 not found. 



The mesophyll is composed of long-celled palisade tissue on the 

 adaxial side and of spongy on the abaxial side which is characterised 

 by large intercellular spaces. The system of large intercellular spaces 

 helps the leaves to float on the surface of water. 



Internal secratory organs are not found. Oxalate of lime occurs 

 in the form of numerous clustered crystals in the spongy tissue. The 

 cells containing clustered crystals are arranged in small groups 

 projecting into the intercellular spaces. Larger clustered crystals are 

 isolated and occur in the palisade tissue. 



The veins are embedded and are not enclosed in bundle-sheaths. 



CUCURBITACEAE 



Momordica dioica Roxb.— Figs. 128, 129, 130. 131. Leaves 

 membraneous. Guard-cells elevated. Mesophyll formed of short- 

 celled palisade tissue on the upper side and of spongy tissue on the 

 lower. Trichomes on the leaf provided with subsidiary cells not 



