52 



inappreciable to the senses, would frequently be sufficient 

 to effect deterioration, it is possible that these impurities 

 may often originate in sources which are least of all 

 suspected. The decomposition of organic matter, whether 

 animal or vegetable, may frequently be the source of in- 

 jurious results in this respect ; for although this is princi- 

 pally resolved into those elementary gases, which appear 

 to form the basis of all created objects, yet there are other 

 matters liberated, which may then enter into fresh combi- 

 nations ; and either this, or a disproportionate accumula- 

 tion, even of these elementary bodies, may reasonably give 

 rise to serious apprehension, and demand the exercise of 

 discretion, in order to prevent them from becoming in- 

 jurious. Besides this, these decomposing bodies, afford 

 just the very state of things, which appears to be requi- 

 site to call into existence, and developement, a numerous 

 phalanx of cryptogamic vegetables : not that such mat- 

 ters, can for a moment be rationally considered to gene- 

 rate, these cellulares-y but that they afford a suitable 

 pabulum, and medium of developement for those millions 

 upon millions of sporules, which we may readily conceive 

 to be dispersed in the atmosphere; and with which it may 

 be teeming, though from their buoyancy and minute- 

 ness, they may float to us invisibly therein. 



The admission of the external air, by the ordinary pro- 

 cess of opening the sashes of forcing houses, has been 

 said to be unnecessary, or at least by no means important, 

 in so far as the function of vegetable respiration is con- 

 cerned, because the buoyancy of the air within all such 

 structures, would enable it to escape in sufficient quan- 

 tity through their openings and crevices, to counter- 

 balance any thing like deterioration, which might by any 

 means result from the vital action of the plant. The ad- 

 mission of external air, is also directly injurious to forced 

 plants, during the winter and spring months, when a very 

 material difference of temperature exists between it, and 



