THE SEED 3 
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, ¢.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 fincly 
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 
hit : * Fics, 8-9. — Different forms of starch grains: 
white oO an egg 18 8, rice; 9, wheat. 
a well-known example, 
and the glutins, which give to the dough of wheat flour and 
ce 
oatmeal their peculiar gummy or “ glutinous ”’ structure. 
