Ch. Ill, 13] USES OF THE PLANT'S FOOD 



101 



The sugars are very nutritive substances, and thus con- 

 stitute reserve food of the highest value to plants. Their 

 qualities, however, make them also good food for animals, 

 which draw freely upon them. Thus, they form the chief 

 food of insects, are an important constituent of the fodder 

 of domestic animals, and give value to the vegetables and 

 fruits used by man, who, however, goes much further in his 

 utilization of them, since A 



he not only systemati- ^ Ift^fflitfM^ 

 cally cultivates and im- 

 proves the plants which 

 produce them most 

 abundantly, but also ex- 

 tracts, refines, and stores 

 them for his own more 

 convenient use. Press- 

 ing out the sweet sap, 

 he boils away the water, 

 obtains the sugar in 

 crystals, and refines 

 them of impurities, a 

 process much easier for 



cane than grape sugar, Fig. 62 a. -Starch grains (concentrically 



for which reason the for- striated) in the cells of Potato; highly 



magnified. (From Figurier.) 



mer is common on our 



tables, while the latter is there unknown. Grape sugar, how- 

 ever, has another economic importance, in that it is the 

 sugar which is fermented to alcohol by the Yeast Plant, 

 though that organism has the power first to convert other 

 BUgars to grape sugar. From this source comes our entire 

 store of alcohol, including all of our wines and strong liquors, 

 as we shall note more fully in the section on fermentation. 



The Starches, also, originate in tranfformations of grape 

 sugar. Their formula is the same as that for cellulose 

 (C 6 HioO & )n, with the n signifying a different number. They 

 are insoluble in the sap, and exist in the plant as solid grains 



