PHENOMENA OF REPRODUCTION. 159 



decomposed; its hydrogen is absorbed ; its oxygen, like that of the air, combines 

 with the carbon of the seed to form carbonic acid, which is set free. Heat is 

 indispensable to germination ; and in the series of phenomena which accompany 

 this process, it acts alternately as cause and effect, for a seed is the theatre of 

 chemical combinations. Light retards germination, by causing the decomposition 

 of carbonic acid, and hence preventing the formation of this gas. Under a 

 combination of favourable circumstances, the seed absorbs water, together with the 

 oxygen of the air ; the albumen, under the chemical action of these agents, loses a 

 portion of its carbon, and at the same time combines with the elements of water ; 

 it soon changes into a saccharine, milky, soluble matter, fit to be absorbed by 

 the embryo; if the albumen has been absorbed previous to germination, the 

 cotyledons enlarge and nourish the plumule. When the latter has emerged 

 from the ground and become green, the phenomena are reversed ; the young plant, 

 instead of absorbing oxygen to combine with its carbon, and disengaging carbonic 

 acid, absorbs carbonic acid, separates the carbon, and assimilates it. 



