THE SEED 



itself. Plants in general require very much the same food 

 that animals do, and they have the power, which animals 

 have not, of manufacturing it out of the crude materials con- 

 tained in the soil water and in the air. Such of these foods 

 as are not needed for immediate consumption, they store up 

 to serve as a provision for the young shoot when the seed 

 begins to germinate. 



3. Food substances contained in seeds. — There are four 

 principal classes of food stored in seeds: sugars, starches, oils, 

 and proteins. The first are held in solution and can be 

 detected, if in sufficient quantity, by the taste. The most 

 important varieties of this group are cane and grape sugar, 

 the latter occurring most abundantly in fruits, the former in 

 roots and stems. Oil usually occurs in the form of globules. 

 It is very abundant in some seeds, e.g. flax, castor bean, and 

 Brazil nut. In the corn grain it is found in the part constitut- 

 ing the germ, or embryo (Figs. 6, 7). Starches and proteins 

 occur in the form of small granules, which have specific 

 shapes in different plants (Figs. 8, 9). Those containing pro- 

 teins are called aleurone grains, and are, as a rule, smaller 

 than the starch grains with which they are intermixed in the 

 bean and some other seeds. In wheat, corn, rice, and most 

 grains they form a layer just inside the husk, as shown in 

 Fig. 10. This is the reason why polished rice and finely 

 bolted flour are less nu- 

 tritious than the darker 

 kinds, from which this 

 valuable food substance 

 has not been removed. 

 The two most familiar 

 kinds of proteins are the 

 albumins, of which the 

 white of an egg is 

 a well-known example, 



and the glutins, which give to the dough of wheat flour and 

 oatmeal their peculiar gummy or " glutinous " structure. 



Figs. 8-9. — Different forms of starch grains ; 

 rice ; 9, wheat. 



