EXTREME CLIMATES. 153 



probable ihat in hot-houses plants will not bear the same 

 quantity of bottom heat as they receive in nature, because we 

 cannot give them the same amount of light and atmospheric 

 warmth ; and it is necessary that we should ascertain experi- 

 mentally 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 chmates, that is to say, where a very high 

 summer temperature is followed by a very low winter tempera- 

 ture. Such countries are Persia, and many parts of the United 

 States, where the summers are excessively hot, and the wiater's 

 cold intense. The seeming impossibility of imitating such 

 conditions artificially will probably account for many of the 

 difficulties we experience ia bringing certain fruits, the Newtown 

 Pippin, the Cherry, the Grape, the Peach, and the Almond, to the 

 perfection they acquire in other countries. 



The great point to attend to in these considerations is the 

 extremes of temperature to which plants are subject when 

 growing; for this reason the calculations of M. Boussingault 

 have less value than might have been anticipated. This disr 

 tinguished French writer upon rural economy proposed, some 

 years ago, a method of determining what amount of heat a 

 plant requires, ia order to be enabled to perform the functions 

 allotted to it by Nature. This method consisted in determining 

 the length of time over which a function extends, and also the 

 mean temperature during that period. Thus, if a given plant 

 requires 20 days to ripen its seeds after flowering, and the mean 

 temperature during that time was 10°, it would be assumed that 

 the plant in question requires 200° of heat to complete the 

 ripening process. Or if the period occupied was 10 days, and 

 the mean heat 10°, then only 100° of heat would be required, 

 and so on. M. Boussiagault's method was a great improvement 

 upon the previous modes of computation. Observers had been 

 previously contented with annual or quarterly, or other long 



