GERMINATION OF SEEDS 8y 
plant in various compounds found in the soil. The white 
of an egg is an illustration of a proteid; and meat in general 
is a proteid food, as contrasted with bread, which is a car- 
bohydrate food. In many seeds proteid food is stored in the 
form of uleurone grains. For example, a section of a wheat 
grain, or the grain of any common cereal, shows aleurone 
grains in the outer layer of endosperm cells, just inside of the 
testa; while the other endosperm cells contain starch grains. 
50. Fats.—In addition to carbohydrates and proteids, 
some plants form fats, the third kind of organic food; and 
these fats are sometimes stored in the seeds in liquid form 
(in small drops), as in the castor-bean, flaxseed, etc. Fats 
contain carbon, hydrogen, and oxygen as do the carbo- 
hydrates; but while in the carbohydrates the hydrogen and 
oxygen occur in the proportion of two to one (H20), in 
the fats the proportion of oxygen is much less. In ad- 
dition to the oil obtained from the seeds mentioned above, 
olive oil and cotton-seed oil may be mentioned as plant 
fats of commercial importance. 
51. Escape of the hypocotyl.—The first part of the 
seedling to push out of the testa is the tip of the hy- 
pocotyl, which 
is to develop 
the root. It 
is soon evident 
that this elon- 
gating tip di- 
rects its growth 
downward, that 
is, toward the 
earth, even if 
it has to curve Fic. 83.—Germinating beans: the bean to the left has not 
been moved; the one to the right was turned 90° after 
about the seed it had reached the stage of the other 
to do so (Fig. 
83). It is exceedingly sensitive to surrounding influ- 
