78 



THE VEGETATIVE EUNCTIONS OE PLANTS 



from the solution, at least as fast as it was made, it would 

 accumulate and thus interfere with the manufacture of 

 more sugar. Some of it is removed at once, either by 

 nourishing the protoplasm of the cell where it was made, 

 or by being translocated to other parts of the plant. But 

 some of the sugar is removed from solution by being 



Fig. s8. — Cell of Pellionia Daveauana, showing starch-grains. The 

 black, crescent-shaped body on the end of each grain is the amyloplasl. 

 Greatly enlarged. (Cf. Figs. 8 and 59.) 



converted into starch, a substance not soluble in water. 

 Thus the accumulation of starch in a leaf or other green 

 tissue indicates that photosynthesis is in progress, and 

 that the resulting carbohydrate is ,or has been formed 

 faster than translocated. The conversion of sugar to 

 starch is accompHshed by certain plastids in the cell 

 (Figs. 8 and 58). 



