352 



FRUITS AND SEEDS 



of liquid food into cellulose, the cell-wall material, wljich, 

 as you noted, is a carbohydrate. The most intricate of 

 all kinds of assimilation is the transformation of food into 

 protoplasm itself, and this building up of the Kving substance 

 is not understood at all. 



e. Mechanics of Germination. — The first external evi- 

 dences of germination are the swelling of the seed, the 

 breaking of the testa, and the emergence of the embryo. 

 Usually small seeds germinate more quickly than large ones ; 

 this seems to be due to the fact that water and oxygen 

 reach all parts of them more readily than is the case with 

 larger seeds. Starchy seeds germinate more quickly than 

 oily ones. The digestion of starch is a more simple process 

 than that of fat. 



In some seeds there are thin spots in the testa through 

 which the embryo emerges. Germination may often be 

 hastened by cutting away pieces of the testa and so mak- 

 ing easier the entrance of air and water and the exit of the 

 young plant. 



Usually the tip of the hypocotyl is the first part of the 

 embryo to appear outside the seed. The advantage of this 

 is evident. The hypocotyl is the water-absorbing part 

 and all the water must come from without. Of food,' on 

 the other hand, there is enough stored within for some 

 time, so that the emergence of the food-making parts is 

 not so pressing a need. 



The cotyledons may appear above the soil or they may 

 not. Germination in which they do appear above the soil 

 is said to be epigean, a word meaning above the soil. When 

 the cotyledons remain below the soil, germination is said 

 to be hypogean. Pumpkin, mustard, beech, and some 

 kinds of beans furnish examples of epigean germination. 



