396 



THICKENING DEPOSITS IN VEGETABLE CELLS. 



Fig. 203. 



suggest, but are merely points at which the deposit is wanting, 

 so that the original Cell- wall there remains unthickened. When 



the Cellular tissue is 

 required to possess 

 unusual firmness, a 

 deposit of Sclerogen 

 (a substance which, 

 when separated from 

 the resinous and 

 other matters that 

 are commonly asso- 

 ciated with it, is 

 found to be allied 

 in chemical composi- 

 tion to Cellulose) is 

 !T;^§g|g. ^^^''^''^T^y^f'^: formed in successive 

 ^w^fe layers, one within 



another (Fig. 203, a), 

 which present them- 

 selves as concentric 

 rings when the Cells 

 containing them are 

 cut through ; and these layers are sometimes so thick and 

 numerous as almost to obliterate the original cavity of the cell. 

 By a continuance of the same arrangement as that which shows 



Tissue of the Testa of the Seed-coat of Star- 

 Anise: — a, as seen in section ; b, as seen on the 

 surface. 



Fig. 204. 



Fig. 20.5. 



Section of Cherry-stone, cutting 

 the Cells transversely. 



Section of Coquilla-nut, in 

 the direction of the long dia- 

 meters of the Cells. 



