NATURE OF PLANTS 



19 



sided as in the potato (Fig. II, B). Frequently two or more 

 grains originate in one leucoplast and compound grains result 

 (Fig. 11, C). Proteids and other foods are likewise transported 

 in solution to the storage organs where they may or may not 

 be deposited in solid form. This is usually effected directly by 

 the protoplasm of the cell without the aid of any plastid. Ani- 

 mals have learned to use the foods stored in these organs just 

 as does the plant. It is interesting, however, to note that we 

 cannot use them as economically as the plant does. In the 



Fig. 11. 



Fig. 12. 



Fig. 11. Starch grains: A, from bean. B, from potato. C, compound 

 grain from potato. 



Fig. 12. Section of the outer portion of a grain of wheat : p, cells con- 

 taining proteid grains. The larger cells are filled with starch. — After 

 Strasburger. 



wheat, for example, the proteid material is largely confined tc 

 the outer portion of the grain (Fig. 12). This layer is of a 

 darker color and in the " best flour " it is excluded in the milling 

 process, leaving the flour very white. So the most nutritious 

 part of the wheat does not appear in white bread, but it should be 

 remembered that white bread is better than the much exploited 

 " whole wheat " products because the proteid material is diges- 

 tible to only a slight degree. These reserve foods are made 

 available to the plant in the same way as to the animal. They 

 are first put into solutions by ferments or enzymes. Saliva in 

 the animal and diastase in the plant are common examples of 

 enzymes which change starch into sugar. So there are enzymes 

 which transform each reserve food and render them capable of 



