THE ESSENTIALS OF AGRICULTURE 



sugar cannot be carried into them, this sugar can be held in the 

 stalk, and we can secure sugar from cornstalks as from sugar cane. 

 In some plants, as in the roots of the sugar beet, sugar is 

 stored in quantity, in the form not of glucose but of cane 

 sugar, or saccharose. However, in most plants sugar is not 

 stored but is carried to growing parts, such as the tubers of the 

 potato, the fruit of the banana, or the seeds of corn and other 

 grains, and is there converted, by means of a chemical ferment, 

 or enzyme, into starch. Throughout the plant kingdom starch 

 is the most common form in which the foods are stored. 



In some seeds, 

 such as those of 

 the castor bean 

 and of flax, and 

 in the flesh of 

 the olive, foods 

 are stored in 

 the form of fats 

 and oils. These 

 are easily de- 

 composed, while 



starch is not easily changed. When needed by the plant the 

 insoluble starch is changed by enzymes, or ferments, into soluble 

 sugar, which is then carried into the growing parts of the plant. 

 Another important form of carbohydrates is cellulose, or 

 woody fiber, which constitutes the framework, or skeleton, of 

 all plant cells. Cellulose is the most stable form of organic 

 matter. This is seen in the power of wood to resist decay. The 

 stems of plants are rich in cellulose and are the last parts of the 

 plant to decay. When eaten by animals, stems are digested less 

 completely and with greater difficulty than grains and leaves. 



In general, the great food storehouses of plants are their 

 seeds (Figs. 16 and 17), in which the foods are deposited and 

 in which the new plant lies embedded. Man has taken advan- 

 tage of this storing habit of plants, just as he utilizes the 

 honey-storing habit of the bee. 



Crown starch 



Horny starch 



Shoot of embryo 



Horny glnten 



Germ 



Root of embryo 



Tip starch 

 Hull 



Tip cap 



FIG. 17. Diagrams of grains of corn 



