346 



FRUITS AND SEEDS 



Fig. 152. — Cells of a potato show- 

 ing starch grains, s; t is a 

 protein crystal. 



Of all the kinds of foods, it is starch which is accumu- 

 lated in the greatest abundance, both in seeds and in 



other plant organs. Potatoes 

 are filled with starch, and the 

 bulk of the seeds of grain is 

 made up of it. (See Figure 149.) 

 Starch occurs in the form of 

 grains. These are microscopic 

 structures marked by concentric 

 rings which are rings of growth, 

 in this respect being somewhat 

 like the rings in wood. (See 

 Figures 152 and 153.) Small 

 starch grains are sometimes 

 found in green leaves. Their 

 presence indicates that the starch has been manufactured 

 more rapidly than it has been transformed into sugar. 

 Usually it is transformed into sugar almost as fast as it is 

 manufactured, and in that soluble form the carbohydrate 

 food moves through the plant body. The 

 starch grains begin to form within the 

 chloroplasts. 



Many seeds are rich in fat in the form of 

 oil drops. Such are the seeds of the castor 

 bean, of cotton, and of the sunflower. 

 From all of these oil is extracted for com- 

 mercial purposes. 



A third form of non-nitrogenous food is 

 the substance of which cell walls is composed. That sub- 

 stance is cellulose. Like starch and sugar, it is one of the 

 carbohydrates. Wood, chemically speaking, is cellulose. 

 It is composed chiefly of the walls of dead cells. The 



Fig. 153. —A single 

 starch grain of po- 

 tato, very highly 

 magnified. Note 

 the concentric 

 rings of growth. 



