112 APPLICATION OF PRINCIPLES. 



"We have, doubtless, much to learn, as to the pro- 

 per manner of applying bottom heat to plants, and as 

 to the amount they will bear under particular circum- 

 stances. It is, in particular probable that in hot- 

 houses plants will not bear the same quantity of bot- 

 tom heat as they receive in nature, because we can- 

 not give them the same amount of light and atmos- 

 pheric warmth ; and it is necessary that we should 

 ascertain experimentally whether it is not a certain 

 proportion between the heat of the air and earth that 

 we must secure, rather than any absolute amount of 

 bottom heat. 



It may also be, indeed it no doubt is, requisite 

 to apply a very high degree of heat to some kinds 

 of plants at particular seasons, although a very much 

 lower amount is suitable afterwards ; a remark that 

 is chiefly applicable to the natives of what are called 

 extreme climates, that is to say, where a very high 

 summer temperature is followed by a very low winter 

 temperature. Such countries are Persia, and many 

 parts of the United States, where the summers are 

 excessively hot, and the winter's cold intense. The 

 seeming impossibility of imitating such conditions 

 artificially will probably account for many of the dif- 

 ficulties we experience in bringing certain fruits, the 

 Newtown pippin, the cherry, the grape, the peach, 

 and the almond, to the perfection they acquire in 

 other countries. 



This subject will be frequently recurred to here- 

 after. 



