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are entirely deprived of any one of them, or 

 even in a much less proportion than they natu- 

 rally require ; though they may linger for a 

 while, it in the end never fails to prove fatal. I 

 have already treated of the three principal ones 

 necessary to our purpose, and shall now proceed 

 to the fourth. Fire, which is here as it were 

 only a secondary agent, used to keep the others 

 in an active state, and is therefore administered 

 in different proportions according to the various 

 degrees of heat necessary to be kept up, in each 

 separate department. 



Very little fire heat seems to be requisite to 

 the preservation of green -house plants, in this 

 climate ; in fact, the less it is found necessary 

 to use, the better. I have never practised it, 

 (except in the case of damps/ as before men- 

 tioned,) until I perceived the frost so severe, as 

 to lower the spirit in the thermometer several 

 degrees below the temperate point, and then 

 merely sufficient to raise it again to the above- 

 mentioned point. If this can be done without 

 the assistance of fire, so much the better, for 

 which purpose, bass mats must be used along 

 the lower parts of the house, where they can be 

 conveniently fastened ; these will be of infinite 



