18 ELEMENTARY ORGANS OE PLANTS. 



produced by the cohesion of their sides. The double nature 

 of the cell-wall may be readily detected by boiling the tissue 

 for a short time, when the cells will separate. In ripe pulpy 

 fruits, the cells may be separately picked out, and examined 

 without boiling. Hence, when pulpy fruits are cut into pieces, 

 there is very little flow of fluid from them, the juices of the 

 fruits being retained in the little membranaceous sacs or cells 

 of which the pieces are composed. 



7. The primitive or typical form of the cells is supposed to 

 be spherical or globular (Fig. 1), and this form the cells 



Fig. 1. 



retain in the lax tissues of succulent plants, in the pulpy parts 

 of fruits, where they do not impress each other, and where 

 growth takes place equally in all directions. But when any 

 part of the plant grows more rapidly in one direction than in 

 another, the cells commonly elongate in that direction, and 

 become elliptical, oblong, or even tubular if free from all adja- 

 cent pressure, and prismatic if laterally compressed, as is the 

 case in young shoots and branches. In the pith and in the 



