296 REMARKS ON THE GERMINATION OF SEEDS. 



Four conditions are necessary for the process of germination : the 

 presence of water, of heat, and of air, and the exclusion of light. 



Water softens the integuments, and renders them capable of being 

 burst by the swollen .embryo; dissolves the nutritive matter contained 

 in the seed, thus reducing it to a fit state to be absorbed for the nu- 

 trition of the embryo ; conveys in solution nutritive particles from 

 other sources ; and furnishes two important ingredients in the com- 

 position of vegetables. 



The air, by means of the oxygen which it contains, effects a che- 

 mical change on the farina of the seed. The oxygen combines with 

 the carbon, and forms carbonic acid, which escapes ; and thus the 

 proportion of oxygen and hydrogen being increased by the expulsion 

 of the carbon, the farina is converted into a semi-fluid substance, of 

 a saccharine or mucilaginous nature, consisting of starch, gum, and 

 sugar, well adapted for the nutrition of the plant in its infant state. 



Heat always promotes chemical combination and decomposition, 

 and thus assists the action of the water in dissolving the hard parts 

 of the seed, and that of the air in its part of the process. Most 

 probably heat acts as a general ^stimulus to the absorbents in the 

 seed. Seeds cannot be made to germinate in very cold weather, 

 except by the application of artificial heat. Too great heat also checks 

 germination, because it destroys the vitality of the seed. 



Light is unfavourable to germination, because it disposes to an 

 accumulation of carbon in the seed, and a consequent hardening of 

 the parts ; or rather prevents the expulsion of carbon, and consequent 

 softening of the parts, which, if necessary, they should be taken up 

 and applied to the use of the plant. The seeds of red poppy and 

 charlock remain in the ground and retain their vitality for a long 

 period ; hence they are frequent on new banks or newly upturned 

 ground. 



From the operation of these causes, it will be seen why seeds 

 planted too deeply in the earth do not germinate. The air has not 

 access to them, and therefore, from the want of that important sti- 

 mulus, they remain torpid. Hence it is that earth newly dug up 

 frequently becomes covered with weeds, the seeds of which soon 

 germinate when exposed to the air. 



Placing seeds at a certain depth in the earth excludes them from 

 the access of light, which is so injurious to germination ; insures a 



