GROWTH AND NUTRITION 19 



observed that cereal plants increase their height J to 

 f after beginning to head, thus showing the rapid growth 

 of the culm during the heading period, and the greater 

 length of the upper internodes, particularly the one bear- 

 ing the spike called the peduncle. The head or spike 

 usually stands at time of full growth of the plant far above 

 the last leaf sheath. In many two-row barleys, however, 

 the spike remains inclosed in the leaf sheath, till after 

 fertilization, and never does entirely emerge. 



18. Ripening. Cereals ripen, on an average, about 

 one month after heading, but sometimes considerably 

 sooner. Ordinarily, for the plant to be ripe, the spikes 

 (or panicles) should be yellow or golden in color, and the 

 straw also yellowishV If the spikes are black when ripe, 

 or any darker color than yellow, the color of the straw 

 will be the chief indication, and the date of ripening may 

 occur sooner than expected. 



NUTRITION 



19. Digestion of reserve food. The growth of the 

 seedling plant proceeds at first entirely at the expense of 

 the reserve food materials in the endosperm (10). These 

 materials are complex, the starch and oils having come 

 to the seed in the simpler form of sugar, and the proteins 

 in the forms probably of sugar and amides. In feeding 

 the embryo there is an interesting reverse process, these 

 complex materials now being re-converted into their 

 previous simpler forms, through the action of unorganized 

 ferments or enzymes. The scutellum, already described 

 (9), is the chief absorbing and converting organ during 

 germination, and furnishes from its epithelial layer (Fig. 

 9) two enzymes, cytase for the breaking down of cellulose 



