GROWTH— NUTRITION. 
97 
would be far more convincing. The author further treats 
of imbibition of oxygen by plants, first observed by Saussure, 
and says, This process has no share whatever in the life of the 
plant. Oxygen is, however, consumed in plants. The scentless 
and tasteless leaves of Agave americana, take up little ; those 
of Pinus ahies, containing oil, more ; those of Quercus rohor, 
containing tannic acid, still more ; among all of them, the bal- 
samic ( n ) leaves of Populus alba most. The author adds, 
that beyond a doubt, and most manifestly, this chemical action 
exhibits itself in the leaves of the Cotyledon calycina, and of 
the Cacalia ficoides, and others. In the morning they are 
acid like sorrel (there is proof of this wanted) ; towards noon 
they are tasteless ; in the evening bitter (not to be perceived). 
A genuine process of oxydatioii, he says, also takes place at 
night ; the acid formed, enters into substances which contain 
hydrogen and oxygen, in the same proportion as in water, or 
that contain less oxygen, as in all tasteless and bitter matters. 
But, on causing Cotyledon calycina to remain the whole day 
in the dark, the reaction of the juice is always acid ; and the 
most simple inference is, that the oxygen, which, when taken 
up, constitutes the acidity, is again secreted when exposed to 
the light. The author likewise asserts, that the exhalation of 
carbonic acid which has been observed, has nothing to do with 
the process of assimilation. The water of the soil contains 
carbonic acid gas, which is taken up by the roots and by the 
leaves, with the water, and is again exhaled. But why is this 
carbonic acid not decomposed, and would it not be a much better 
source of sustenance than the atmosphere itself ? Is the whole 
of the carbonic acid of the atmosphere really decomposed ? 
I by no means wish to dispute the principal fact, but would 
suggest, that the dictatorial manner assumed by the author, 
must render his conclusions suspicious. The author is quite 
angry, that the talent and ability of Botanists should have been 
wasted in the investigation of the structure and the external 
forms of plants, whilst chemistry and physiology have been 
neglected, in the explanation of the most simple processes. As 
a proof, he quotes Beum’s Forest Botany, and a sentence from 
Burdach’s Physiology. Why these, above all ? It certainly 
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