OF ATMOSPHERICAL TEMPERATURE. 149 



a plant ; if the temperature is at the same time high, 

 excitability will remain in a state of continued action, 

 and that rest which is necessary (113) will be with- 

 held, the result of which will be an eventual destruc- 

 tion of the vital energies. But, on the other hand, if 

 the temperature is kept low while the amount of 

 atmospherical moisture is considerable, the latter is 

 absorbed, without its being possible for the plant to 

 decompose it ; the system then becomes, in the 

 younger and more absorbent parts, distended with 

 water, and decomposition takes place, followed by 

 the appearance of a crop of microscopical fungi ; in 

 short, that appearance presents itself which is techni- 

 cally called <; damping off." 



The skilful balancing of the temperature and mois- 

 ture of the air, in cultivating different kinds of plants, 

 and the just adaptation of them to the various seasons 

 of growth, constitute the most complicated and dim- 

 cult part of a gardener's art. There is some danger 

 in laying down any general rules with respect to this 

 subject, so much depends upon the peculiar habits of 

 species, of which the modifications are endless. It 

 may, however, I think, be safely stated, that the fol- 

 lowing rules deserve especial attention : — 



1. Most moisture in the air is demanded by plants 

 when they first begin to grow, and least when their 

 periodical growth is completed. 



2. The quantity of atmospheric moisture required 

 by plants i£, coeteris paribus, in inverse proportion to 

 the distance from the equator of the countries which 

 they naturally inhabit. 



