THE LADIES* MAGAZINE OF GARDENING. 315 
rays; of their deoxidating power we shall have abundant evidence in the 
next section. 
8 . Condition of plants, with regard to air , in close cases and in the free 
atmosphere .—In the last place, we have to treat of the state or condition 
of the air which contributes to the support of vegetation in these plant- 
cases. Mr. Ward appears to think that the air suffers no other change 
than that of “ expansion by heat. With every change of temperature, a 
corresponding change,” says he, 66 takes place in the volume of air; and 
without such variation the plants would soon perish.” Besides a change 
of volume in the way above mentioned, it is, however, certain that the 
air in these cases must also undergo a change of composition, which gra¬ 
dually impairs, and would ultimately destroy, its power of supporting 
vegetation. Unless, therefore, fresh air be supplied to replace that which 
may have been injured by the vegetative process, or means be found of 
restoring the deteriorated portion to its former purity, vegetation cannot 
long continue. Though the cases in which the plants are confined may 
not be perfectly air-tight, yet they are made so close as to prevent that 
amount of change in the air which is required for healthy vegetation ; and 
we must, therefore, seek for other means by which a wholesome state of 
the atmosphere may be maintained. As the mode in which this object is ac¬ 
complished is somewhat perplexing, and opinions concerning it are much 
at variance, we may, perhaps, be excused for going a little farther into 
detail on this point than we should otherwise have done. 
The experiments of various chemists, from Scheele down to De Saussure, 
have shown that seeds do not germinate without receiving continual 
supplies of fresh air, and that in the progress of their evolution they 
convert the oxygen gas of such air into an equal volume of carbonic acid 
gas. As plants spring from seeds, it was natural to expect that to carry 
on their progressive development they would also require fresh air, and 
would in like manner convert its oxygfen into carbonic acid gas. Both 
these facts were proved by Dr. Ingenhousz in his Experiences sur les 
Vegetaux , t. ii. p. 35-37; by M. Senebier, in his Physiologie Vegetale , 
t. iii. p. 113; and by Theodore de Saussure, in the Annales de Chimie , 
t. xxiv. p. 139. M. Senebier farther maintained that the air thus employed 
in vegetation, lost precisely the quantity of oxygen gas necessary to the 
formation of the carbonic acid gas produced, a result confirmed by the 
experiments of De Saussure and by those of other writers; so that in the 
progressive stages of development and growth, plants, like the seeds from 
which they sprang, not only require a pure air, but convert a portion of 
its oxygen into an equal volume of carbonic acid gas. 
(To be continued.) 
