GERMINATION. 51 



gen of the air. Hence, as the acid is often produced in the 

 soil, in larger quantities than in the air, some have ascribed 

 the favorable influence of lime and alkalies upon germination 

 to the fact, that they absorb carbonic acid. 



For a similar reason seeds should not be sown, or planted 

 in direct contact with green or fermenting manures, as the 

 process of fermentation evolves large quantities of carbonic 

 acid, in addition to that which the seed gives out in the pro- 

 cess of germination. This view has been given to explain 

 a fact which farmers have learned by experience, that when 

 green manures are placed in the hill, the corn planted upon 

 it, will not come up so well, as when the manure is spread, 

 and incorporated with the soil. But it is impossible to see 

 why the carbonic acid produced in this process should not 

 prove beneficial rather than injurious, for this acid is imme- 

 diately employed to decompose the rocks, and eliminate the 

 potash, or other alkalies, which are required to render the 

 food soluble, and fitted to be absorbed by the plant, the in- 

 stant its organs are sufficiently developed to receive it from 

 the soil. The more probable reason for the injurious effects 

 of green manures upon the soil is, that they impart too much 

 nourishment, and injure the plant, by yielding more food than 

 its organs, in this incipient state, can digest. 



3. Heat. The third condition necessary to germination, 

 is a proper temperature. No seed has been known to ger- 

 minate at, or below the freezing point of water ; hence, seeds 

 do not germinate during the winter, although all other con- 

 ditions are supplied. The vital principle, however, is not al- 

 ways destroyed, but is developed on the return of spring, 

 when the temperature has arrived at the proper degree. The 

 requisite degree of temperature varies from 60° to 80° F. 

 The precise temperature depends upon the nature of the 

 seed, or plant. This accounts for the fact, that different 

 seeds germinate at different seasons of the year ; hence the 

 importance to the farmer of ascertaining the degree of tern- 



