GERMINATION OF SEEDS 



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 alcurone 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 (H 2 O), 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 

 about the seed 

 to do so (Fig. 

 83). It is exceedingly sensitive 



FIG. 83. Germinating beans: the bean to the left has not 

 been moved; the one to the right was turned 90 after 

 it had reached the stage of the other 



to surrounding influ- 



