58 Vegetable Organography and Physiology. 
renovated in passing through the leaves, by its combinations with 
atmospheric air, returns, and, like the arterial fluid, penetrates ev- 
ery part of the vegetable fabric, and deposits in each tissue its 
appropriate nourishment. 
In glancing thus briefly at the organisms and functions of ani- 
mals and vegetables, it will be seen that there is identity of struc- 
ture and unity of function existing, throughout, between the two 
kingdoms. ‘ Perhaps,” says Professor Henslow, “until the con- 
trary shall have been proved, we may consider the addition of 
sensibility to the living principle, as the characteristic property of 
animals.” But as he defines this characteristic property of an- 
imals to be “a quality by which the individual is rendered con- 
scious of its existence, or of its wants, and by which it is indu- 
ced to satisfy those wants by some act of volition,’’* we are in- 
clined to the belief, however difficult it may be to demonstrate 
it, that a quality strictly analogous, in its a: to this property 
in animals, belongs to vegetables ! 
_ During a residence of several years in the country, we have 
“watched the growth and studied the habits of some of the ex- 
ogenous plants, with the highest interest; and it is our intention 
to close this paper with some observations made upon one of the 
most common specimens of exogenous trees. 
_ Itis well known to botanists that some species of plants attach 
themselves, apparently from choice, to barren surfaces, and veg- 
etate with surprising vigor. They even possess the power of ex- 
cavating crevices for the attachment of their roots in the calcare- 
ous rocks to which they fasten themselves. This is the case with 
some tribes of lichen. Possessing the power of secreting an aci 
from their roots, which acts upon the carbonate of lime, they are 
thus enabled gradually to imbed themselves into the surface of the 
rock itself Some trees, also, of the exogenous class, as the 
Ulmus Americana, or common elm of this country, not only flout 
ish best in mountainous regions, and where the soil is thin, but 
they are often seen growing upon the limestone ledges, where 
but little soil is found for the attachment of their roots. One of 
_ these trees had sprung up, and had attained some magnitude, 0? 
: = thinly soil-clad surface, and near the edge of a broad calee 
* Principles, page 8. + Roget, page 39, et seq. 
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