THE VEGETABLE KINGDOM. 



483 



solutely necessary to vegetable evolution, and that if the 

 great chemist stated the contrary it could only be attrib- 

 uted to the defective construction of his instruments, which 

 enabled him to obtain but a very imperfect vacuum. 



All the air, however, is not employed in the first phase 





mum 





207. Roots Lighted from below and directing themselves towards the Light. 



of vegetable life ; of its two principal elements the oxygen 

 is here alone of service. It is to the chemist Scheele that 

 the glory of this great discovery is due. 



Some seeds only absorb a small quantity of it ; one or two 

 thousandths of their weight is enough ; this is the case with 

 wheat. Others, such as the haricot bean, consume, accord- 



