GERMINATION 139 



moisture and manages to burst its cell. Therefore, 

 to shorten the period of germination care is taken to 

 thin the shells of excessively hard seeds by rubbing 

 them with a stone. 



"Besides the mechanical part played by water in 

 opening the seed, it has still another relating to nu- 

 trition. The various changes undergone by the ali- 

 mentary contents of the perisperm and the cotyle- 

 dons in becoming liquefied and capable of absorption 

 cannot take place without the aid of water. Fur- 

 thermore, this liquid is indispensable for dissolving 

 the nutritive ingredients, introducing them into the 

 young plant, and distributing them evenly through- 

 out. It is plain, then, that if the seed remains dry 

 it is absolutely impossible for it to germinate, and 

 that in order to preserve seeds the first condition is 

 to protect them from moisture. 



"With moisture there must also be warmth. As a 

 general rule, germination proceeds most satisfac- 

 torily when the thermometer registers between ten 

 and twenty degrees centigrade, our spring and au- 

 tumn temperature. Outside these limits, be it above 

 or below, germination is retarded, ceasing altogether 

 in extreme temperatures. 



"The cooperation of air is not less necessary. 

 Seeds might have the proper temperature and suf- 

 ficient moisture, but if air were lacking germination 

 would not follow. This capital condition explains 

 to us why seeds planted too deep fail to come, up ; 

 why germination is much easier in soil that is mellow 

 and can be permeated by the air than in soil that is 



