86 A TEXT-BOOK OF BOTANY 



of the hypocotyl is a bud, called the plumule, from which 

 the future leafy stem is to develop. In many seeds the 

 reserve food is not stored in the cotyledons, but in a spe- 

 cial tissue surrounding the embryo, which in general may 

 be called endosperm. In the violet seed, for example, 

 within the testa is the endosperm, and embedded in the 

 endosperm lies the embryo (Fig. 8 la). 



44. Conditions for germination. The length of time 

 seeds may retain their vitality varies with different plants. 

 In nature they are expected to germinate in the growing 

 season following their maturity; but many are known to re- 

 tain the power of germination for several years if kept in 

 proper conditions, chief among which, apparently, is dry- 

 ness. The stories of the germination of wheat and corn ob- 

 tained from the wrappings of mummies have proved to be 

 myths. 



The conditions required for germination are abundant 

 moisture, suitable temperature, and a supply of oxygen 

 (which means access of air). Seeds vary greatly in the 

 amount of heat necessary for germination, as may be 

 inferred from the fact that some seeds germinate in early 

 spring or even on the melting snow-fields of alpine and 

 arctic regions, while others need the heat of the tropics. 



45. Absorption of water. When a seed has been placed 

 in the proper conditions for germination, the first visible 

 result is its swelling through the absorption of water. The 

 amount and force of this swelling may be observed by plac- 

 ing a quantity of seeds in a tumbler of water and putting 

 various weights on the mass. It is entirely clear also that 

 oxygen has been passing in, for the seed gives off carbon 

 dioxide and heat. That heat is given off by a germinating 

 seed is made very plain in the process of malting, in which 

 a large mass of barley is put in germinating conditions in a 

 confined space, and the combined heat from all the seeds 

 becomes very evident. 



