93 



CHAPTER XL 



THE PROCESS OF VEGETATION. USE OF 

 THE COTYLEDONS. 



When a seed is committed to the ground 

 it swells by the moisture v/hich its vessels 

 soon absorb, and which, in conjunction with- 

 some degree of heat, stimulates its vital prin- 

 ciple. Atmospherical air is also necessary to 

 incipient vegetation, for sseds in general will 

 not grow under water, except those of aquatic 

 plants, nor under an exhausted receiver; and 

 modern chemists have determined oxygen 

 gas, which is always an ingredient in our at- 

 mosphere, to be absorbed by seeds in vege- 

 tation. An experiment is recorded in the 

 Philosophical Transactions, No. 23, of sow- 

 ing Lettuce-seed in two separate pots, one of 

 which was placed in the common air, the 

 other in the vacuum of an air-pump. In the 



