294 MANAGEMENT OF THE ATMOSPHERE. 



evil they call stagnation, and denounce the system of sealing up 

 plants (as some of them have termed it) from all atmospheric 

 influence but that exerted over them by their own tainted arti- 

 ficial atmosphere. Now, a stagnant atmosphere, or any con- 

 dition in the atmosphere of a hot-house approaching to stagna- 

 tion, certainly cannot be otherwise than injurious to vegetation. 

 This is a statement the truth of which will scarcely be called in 

 question. But, although the prevention or removal of it has 

 always been the chief object of every scientific gardener, it can- 

 not be said that every gardener, having this aim in view, has 

 taken the right way to effect his purpose ; for, certainly, what 

 is called "free" ventilation is very far from being the proper 

 mode of obviating the evil ; and, in questioning the propriety 

 of the system upon these grounds, it may be deemed necessary 

 to enter into an explanation of the results attributed to this sys- 

 tem of ventilation, which is said to be requisite in order to 

 adapt an artificial air to the circumstances of the plants growing 

 in it, and which is supposed by some to be in exact harmony 

 with the laws of vegetable physiology, and with all that science 

 has unfolded to us respecting the effects of the atmosphere upon 

 vegetable life. 



The direct effects of ventilation, of any description, are two- 

 fold, mechanical and chemical. The former embraces the influ- 

 ence which motion possesses over the growth of plants ; and this 

 influence has never yet been accurately defined or explained 

 whether it be injurious or beneficial, and in what particular 

 degree it ceases to be so. The latter comprehends the effects of 

 the various gases, and their influence upon the vital functions 

 of vegetable beings. To illustrate the effects of the first of 

 these agents, viz., motion, we may refer to the circumstance 

 that is well known, that trees trained upon a wall, in ordi- 

 nary circumstances, do not grow to such size as those standing 

 in isolated places ; but their fibre is sooner matured, and also 

 their fruit earlier, as well as larger and more saccharine. It has 

 been asserted that wall trees do not arrive at so great an age as 

 others standing in exposed situations, an assertion as founda- 

 tionless as it is absurd ; for it is a well-known fact, that wall trees 

 have outlived others of the same kind, planted in similar soil, 



