180 APPLICATION OP PEINCIPLES. 



seed to that which is best suited for the growth of the 

 embryo (103) ; then, if the embryo is so situated that it 

 cannot obtain from the surrounding medium food upon 

 which to subsist, its germination stops, and; being de- 

 prived of its carbon, the safeguard of its vitality is re- 

 moved, and it perishes. If, however, the amount of 

 moisture in contact with a seed is very small, as in the 

 dry earth at the bottom of a tumulus for instance, the 

 temperature at the same time lfcw, and the access of at- 

 mospheric air cut off, neither putrefaction nor germi- 

 nation is likely to occur. If seeds are exposed to a 

 high temperature in dryness, they will not perish un- 

 less the temperature rises beyond anything likely to 

 occur under natural circumstances. Edwards and 

 Colin found that even wheat, barley, and rye, inhabit- 

 ants of temperate countries, would bear when dry 104° 

 for a long time without injury, although they died in 

 three days in water at 95° ; and a much higher pro- 

 longed temperature may be expected to produce no 

 ill effect upon seeds inhabiting hotter countries. 

 There is no apparent reason why the exposure of dry 

 seeds to the air should destroy vitality, unless the ex- 

 posure is very much prolonged ; nor have we any 

 evidence to show that it does, so long as they remain 

 dry. The way in which the atmosphere would act 

 injuriously upon dormant seeds is, by its oxygen ab- 

 stracting their carbon ; and it was formerly supposed 

 that the carbonic acid extricated by germinating seeds 

 was formed in this way. But the very valuable ob- 

 servations and experiments of Messrs. Edwards and 

 Colin (see Comptes rendus de VAcadSmie des Sciences, 



