18 



STORAGE OF FOODS 



sugar so that by morning the cells are quite emptied of the sugar 

 and ready for another day's work. This accumulation and trans- 

 fer of foods can easily be demonstrated by cutting off in the 

 afternoon leaves from clover, bean or other starch-forming plant 

 and placing them in alcohol. When blanched and tested with 

 iodine the blue or blue-black color shows that they have accumu- 

 lated a large amount of starch. Test in the same way leaves 

 taken from these plants early in the morning. No starch re- 

 action will be seen because the cells have been freed from their 

 starch during the night. The formation of starch is often used 

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

 photosynthesis first results in the formation of various sugars 

 and that starch only appears when the sugars have reached a 

 certain percentage in the cells and indeed that some plants do 

 not form starch at all. So when starch appears in a leaf it is 

 simply the measure of the excess of carbohydrate manufacture 

 over transportation. Furthermore starch will form in the cells 

 in the dark if a plant is supplied with an excess of carbohydrate. 

 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, 



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

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



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 re- 

 newal of growth. They generally assume much more definite 



