12 EKINCIPLES OF GARDENING. [CH. I. 



power the longest, and for the evident reason, that 

 such ai'e less prone to decay. 



At the same time, let me guard myself from being 

 misconceived to say, that such are the only chemical 

 causes for a seed's curtailed or protracted vitality. 

 On the contrary, I am "well awai'e there are others, 

 and for example may be taken many seeds abounding 

 with expressed oil. These, exposed to the free ope- 

 ration of the air, gradually lose their \'itality, as the 

 oil they contain becomes rancid. Presented from the 

 action of the air, no seeds are more retentive of vi- 

 tality, apparently because when so preserved, the oil 

 they contain will remain sweet and unchanged for 

 ages. This is the reason that in earth excavated 

 from great depths below the sui-face, charlock, mus- 

 tard, and such like plants, ha\ing oleaginous seeds, 

 are found to have retained their embiyo ^^tality. 



In considering this subject, let it ever be kept in 

 mind, that almost every species of seed has a peculiar 

 degree of heat, and a peculiar amoimt of moisture, 

 at or approaching to which its vitality will be excited 

 into action. Therefore, in all obsei'vations on the 

 life-retaining power of seeds, and in conclusions 

 deduced from experiment, it must be carefully 

 secured that they have not been excited to those 

 initiatory steps of germination, which being taken and 

 then checked, invariably cause the destruction of a 

 seed's vital powers. 



