51 



moisture from the plants, until its capacity is satisfied ; 

 and hence the plants are rohbed of their " life's blood." 

 Besides this action, which is the cause of serious evil, the 

 tissue itself is contracted and thereby injured, by reason 

 of the degree of cold, which is at the first gush, liable to 

 come in contact with the warm foliage. These remarks 

 apply to cold air, when admitted in a large bulk, by open- 

 ing the sashes ; and when a draught is produced, by open- 

 ing them, both at the back and front, and the top and 

 bottom of the house. 



Deterioration of the air, by the action of the functions 

 of the plants, could not take place, except in hermetically 

 sealed structures : for by reason of the expansibility and 

 elasticity of air, when it becomes at all heated, it not only 

 gains egress, but also admission through the most minute 

 crevices: that this interchange is sufficient to counteract 

 any deteriorating influence which the plants might have on 

 the internal air, with respect to their continued existence 

 in it, is abundantly proved by the growth of plants in 

 Ward's cases, from the interior of which the external air 

 is excluded as fully as it possibly can be, without their 

 being actually sealed : if therefore, any injurious effects 

 result to plants, from their being cultivated in a close 

 atmosphere, we must seek for the cause, in some other 

 source, than the plants themselves. If any noxious quali- 

 ties exist in the atmosphere of structures, to which the 

 external air has not free ingress, they must result from 

 some neglect or ignorance on our part, in suffering extra- 

 neous and unwholesome matters to accumulate in such 

 situations, and there to decompose, and enter into combi- 

 nation with those gaseous bodies, which form the volume 

 of the internal atmosphere of our plant structures. The 

 existence of such extraneous matters, may indeed be 

 traced to various sources ; and they may be present, even 

 when much vigilance is employed to prevent their accumu- 

 lation; and therefore, as an inconceivably minute quantity, 



