yiO THE UNIVERSE. 



this structure that principally gives access to the water 

 which is so indispensably necessary to primordial life. 



The air also plays a great part in the chemical pheno- 

 mena of germination. The learned Homberg denied the 

 importance of it, because he saw seeds develop in the 

 receiver of his pneumatic machine. But Boyle, jNIuschen- 

 broeck, and Boerhaave demonstrated that this agent is 

 absolutely necessary to vegetable evolution, and that if the 

 great chemist stated the contrary, it could only be attri- 

 buted to the defective construction of his instruments which 

 enal^led him to olitain but a A'ery imperfect vacuum. 



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

 of vegetal:)le 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 rpiantity of it ; one or 

 two thousandths of their Aveight is enough ; this is the case 

 with wheat. Others, such as the haricot bean, consimie, 

 according to Saussure and Woodhouse, as much as a 

 hundredth part. 



At the time when seeds germinate they exhale carbonic 

 acid and water, and set free a noticealDle amount of 

 heat. 



Divers causes accessorily hasten the evolution of the 

 plant. 



Electricity is one of these. It was the Abbe NoUet who 

 discovered its action. More recently Sir Humphrey Dayj 

 and A. Becquerel observed that it is only negative elec- 

 tricity that gives energy to this phenomenon; whilst positive 

 electricity, on the contrary, retards it. 



Indeed, if Ave pass an electric current beneath a soAvn 

 surface, the seeds develop much more quickly than in a 

 imrt which has not been submitted to electricity. 



