ASSIMILATION. Ill 



by de-oxydizing processes, the fluid contents of the cells, 

 such as gum and sugar, chromule, the fixed and volatile 

 oils, organic acids, &c., are the results of oxydation. Starch 

 and chlorophyl are therefore the products of vegetable di- 

 gestion, the other substances of vegetable respiration. This 

 will be clearly seen if we consider the nature of these sub- 

 stances. They are of great importance in the vegetable 

 economy, and must be carefully studied if we would obtain 

 correct views of the nutrition of plants. 



Starch is one of the most abundant and useful products 

 of vegetation. It exists in the seeds, roots, and stems of 

 plants, and in the pulp of fruits ; for whilst chlorophyl is 

 formed only on the outer surface of plants, starch is re- 

 Fig. 22. 





a. Club-shaped granules in milky juice of Euphorbia splendens. b. Three 

 of the lactiferous vessels, with starch granules in situ. QUEKETT. 



stricted to their interior, light being absolutely necessary 

 in the one case and darkness in the other. Starch exists 

 in the cells of plants in the form of transparent 'and color- 

 less granules, which vary in figure and size in different 

 species. They are for the most part of an ovoid shape ; 

 but, in the Euphorbiacese, their shape is like an elongated 



