Full text: Vol. IV. (4)

246 
Book IV. 
Plants re 
mnine lond 
Water ne 
cessary. 
VEGETATION, 
we examine this increase more minutely, we find that a 
new layer of wood, or rather of alburnum, has been 
added to the tree in every part, and this addition has 
been made just under the bark. We find, too, that a 
layer of alburnum has assumed the appearance of per 
fect wood. Besides this addition of vegetable fibre, a 
great number of leaves have been produced ; and the 
tree puts forth flowers, and forms seeds. 
It is evident from all this, that a great deal of new 
matter is continually making its appearance in plants. 
Hence, since it would be absurd to suppose that they 
create new matter, it must follow that they receive it 
by some channel or other. Plants, then, require food 
as well as animals. Now, what is this food, and whence 
do they derive it? These questions can only be an 
swered by an attentive survey of the substances which 
are contained in vegetables, and an examination of those 
substances which are necessary for their vegetation. If 
we could succeed cómpletely, it would throw a great 
deal of light upon the nature of soils and of manures, 
and on some of the most important questions in agricul 
ture. But we are far indeed at present from being able 
to examine the subject to tie bottom. 
1. In the first place, it is certain that plants will not 
vegetate without water; for whenever they are deprived 
of it, they wither and die. Hence the well-known use 
of rains and dews, and the artificial watering of ground. 
Water, then, is at least an essential part of the food of 
plants. But many plants grow in pure water; and 
therefore it may be questioned whether water is not the 
only food of plants. This opinion was adopted very 
long ago, and numerous experiments have been made in 
order to demonstrate it. Indeed, it was the general opi¬
	        
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