NATURE OF PLANTS 



19 



very regularly construced starch grains (Fig. 10, A). In the 

 pea seed and in wheat and other grains proteid granules are 

 associated with the starch grains (Fig. 10, B). These starch 

 grains are formed by rather colorless plastids called leucoplasts 

 (Fig. 3, E) that closely resemble the chloroplasts. The starch 

 grain first appears in the leucoplast as a minute point. Its strati- 

 fied structure is due to the successive deposits of starch by the 

 leucoplasts. If the grain is built up equally on all sides by the 

 leucoplasts it will possess regular and concentric strata as in the 

 bean (Fig. 11, A). If the bulk of the leucoplast lies on one 

 side of the grain, this side of the grain will receive more material 

 and consequently the starch grain will become more or less one- 



FlG. II. 



Fig. 12. 



Fig. II. 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: ^, cells containing 

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



sided as in the potato (Fig. 11, B). Frequently two or more 

 grains originate in one leucoplast and compound grains result 

 (Fig. II, 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 

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

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



