i8 



STORAGE OF FOODS 



as a test for photosynthesis, but it must be borne in mind that 

 photosynthesis results in the formation of various substances, 

 and that some plants indeed do not form starch at all. 



10. The Storage of Foods. It has been stated that the foods 

 not required for the nourishment and growth of the plant are 

 stored in the region of buds, the growing portions of stems, 

 in bulbs, in roots, in seeds, and in fruits. These are the so- 

 called storage foods and they remain in these regions for con- 

 siderable periods or until the conditions are favorable for a 

 renewal of growth. They generally assume much more definite 

 forms than the products constructed in the chlorenchyma which 

 were designed for immediate use or translocation to other parts. 

 If we examine a potato the cells will seem to be filled with 

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



B. 



FIG. 10. Storage food : A, starch grains in cell of potato n, nucleus. 

 B, cells of bean, the smaller particles being proteid grains. 



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. n, 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- 



