GERMINATION. 



79 



earth remains a long time covered with standing water, 

 the seeds must decay, and also, that a seed placed in dry 

 earth cannot germinate unless it be moistened. 



The impossibility of a seed's germinating, when too 

 deeply buried in the ground, explains why we sometimes 

 see, after deep tilling, plants making their appearance, of 

 the same kind as those which had been cultivated upon 

 the soil several years before. The state of the earth as it 

 regards moisture, at the time of sowing, furnishes a reason, 

 independent of the action of heat, why seeds are a longer 

 or shorter time in sprouting. 



Seeds do not germinate in pure carbonic acid. Mixed 

 with atmospheric air this gas retards the process of ger- 

 mination ; but it may be hastened by absorbing the car- 

 bonic acid evolved by the seeds, by means of lime or 

 alkalies. 



During the first stages of vegetation the feeble plant 

 rejects those other aliments which, as it advances in 

 strength, become the principal agents in its nutrition. 



Germination takes place in the same space of time in 

 darkness as in light. But M. de Saussure has observed, 

 that, after the process of germination was completed, the 

 developement of plants was more rapid and perfect in the 

 light than in obscurity. 



Thus we see, that, in the germination of seeds, every 

 thing may be reduced to the following facts. 



Water, or moisture, swells the seed, and the oxygen 

 contained in that liquid subtracts from the seed the 

 carbon which is its principal constituent. 



The swelling of the seed by water facilitates the intro- 

 duction of atmospheric air into the interior of the grain, 

 where its oxygen can combine more readily with the 

 carbon for the formation of carbonic acid, which is dis- 

 engaged under the form of a gas. 



The heat necessary for germination facilitates the ac- 

 tion of the oxygen and the volatilization of the carbonic 

 acid gas, at the same time that it excites the germ and 

 stimulates its developement. 



The subtraction of a portion of their carbon changes 

 the state and the nature of seeds. The mucilage and the 

 starch, of which they are almost entirely composed, by 

 parting with a portion of their carbon, pass to the state of 

 sweetish^ milky substances, containing sugar, which is 

 the first nourishment of the embryo plants. 



