176 APPLICATION OF PRINCIPLES. 



being ripe, these conditions are not secured ; and, in 

 proportion to the deficiency of carbon and superabun- 

 dance of water, is the seed liable to perish. 



The complete maturation of the seed is, however, a 

 disadvantage, when it has to be sown immediately 

 after being gathered ; for the embryo is formed, and 

 capable of germinating, long before the period of 

 greatest maturity. There are two periods in the 

 latter part of the organisation of a seed which, 

 although separated by no limits, require to be distin- 

 guished. The first is that when the embryo is com- 

 pleted ; and the second is when nature has, in ad- 

 dition, furnished it with the means of maintaining 

 its vitality for a long period. It is just as capable of 

 growing at the expiration of the first period as of the 

 second ; it will do so immediately if committed to the 

 ground, and we see it actually happening to Peas, 

 Beans, Com, and other field crops, in wet summers ; 

 but, at the end of the second period, it cannot germi- 

 nate till it has relieved itself of all the carbon which, 

 during that period, was deposited in its tissue. 



If seeds are to be preserved for a length of time, a 

 state of complete dryness is so necessary to them that 

 it has been recommended to increase it by artificial 

 means : not, however, by the application of heat, or 

 by any process like that of kiln-drying, for that would 

 destroy their vitality ; but by some of those chemical 

 processes which dry the atmosphere without raising 

 its temperature. It occurred to Mr. Livingstone, that 

 air made dry by means of sulphuric acid might be 

 advantageously employed for this purpose, and he 



