MEMOIR XI.] THE FORCE INCLUDED IN PLANTS. 179 



for them in the preceding year by the parent plant, and 

 stored up for their use, but their leaves, expanding, turn 

 green, and expose themselves to receive the rays of the 

 sun. If they be now examined as in the previous in- 

 stance, making allowance for the water they contain, it 

 will be found that from day to day their weight is in- 

 creasing; they are living independently of the seed. 

 They are obtaining carbon and hydrogen, the former 

 from carbonic acid, and the latter from water and am- 

 monia compounds existing in the air or furnished from 

 the ground. 



If a seedling, germinated in darkness and permitted to 

 grow to a certain extent, be then exposed to light, pro- 

 vided its dark -life has not continued too long, its etio- 

 lated aspect will soon disappear ; it turns green, and as- 

 sumes all the characters of a healthy plant. This is in 

 effect the natural process. For we bury seeds a little 

 under the surface, covering them lightly with earth, the 

 opacity of which secures the necessary darkness ; but the 

 mould being moist, the air having a ready access, and 

 the temperature of the season suitable, all the conditions 

 needful for germination water, air, warmth, darkness 

 are present. The plumule, or shoot, makes its way out 

 of the obscurity into the light; its reliance for nutrition 

 on the seed ends; its independent life begins. It obtains 

 carbon, hydrogen, oxygen, nitrogen from the air, and sa- 

 line substances and water from the soil. 



The facts which we thus bring into relief, as necessary 

 for the further exposition of the subject, are these : In 

 the first stage of the life of a plant, its dark -life, there 

 is, excluding water, a diminution in the weight; in the 

 second, or light-life, there is an increase, due very largely 

 to the appropriation of carbon from the air. The atmos- 

 pheric carbonic acid has been decomposed, its oxygen set 

 free and, for the most part, permitted to escape, its other 



