202 



BOTANY: PRINCIPLES AND PROBLEMS 



Seed Germination. — The seed remains dormant until a favor- 

 able environment appears, when the embryo begins to grow 

 and the seed is said to (jerminate (Fig. 117). The conditions 

 necessary for germination are a plentiful supply of water and 

 oxygen and a moderately high temperature. When these are 

 fulfilled, metabolism begins vigorously in the embryo and in the 

 cells of the endosperm. Water is absorbed in large quantities 



Fig. 117. — Germination of the seed. A, the bean. 1, embryo of seed. 2, 

 young seedling, the cotyledons raised aljove the ground and the plumule begin- 

 ning to develop. 3, older seedling. .B, the pea. 1, embryo of seed. 2, seedling. 

 The cotyledons here remain in the ground, only the plumule growing upward. 

 {From Gray) . 



and the embryo swells, bursts the seed coats, sends its root into 

 the ground and its stem into the air, and becomes a seedling. 

 The food stored in endosperm or cotyledons is digested and used 

 for the development of new organs. It is generally sufficient in 

 amount to provide for the growth of the seedling to a point where 

 the latter can begin to manufacture its own food. Indeed, as 

 soon as the young stem and leaves get above the ground they 



