DISPERSAL AND GERMINATION OF SEEDS 177 



109. Food-storage. -- Thus far, only the carbohydrate 

 starch has been mentioned as a food-storage form in seeds, 

 and it is the most common form in the seeds used for food by 

 men. But another conspicuous group of foods are the proteins 

 (see 29, p. 37), and carbohydrates are used in the manufact- 

 ure of proteins before protoplasm can be reached. In some 

 seeds proteins are stored in the form of little grains (aleurone 

 grains). For example, in a " grain " of wheat (or of any 

 ordinary cereal), the outer layer of endosperm cells contains 

 aleurone grains, and the other endosperm cells contain starch 

 grains. In some seeds, food is stored in the form of fats 

 in liquid form (oils). Fats contain the same chemical ele- 

 ments (carbon, hydrogen, and oxygen) as do the carbohy- 

 drates, but not in the same proportion. Well-known oils 

 obtained from seeds are castor-oil, linseed oil (from flax), 

 cottonseed oil, and olive oil. 



FIG. 145. Germinating beana, showing the hypocotyl ; 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, and has developed a curve in response to the stimulus of gravity. 



110. Escape of the hypocotyl. All of the processes 

 described above as connected with germination are prelimi- 

 nary to the emergence of any part of the embryo from the seed. 

 It was stated that growth is most active at first in the hypo- 

 cotyl, whose tip is always directed towards that point in the 

 seed-coat where the micropyle of the ovule was situated, and 



