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 results, 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. 



It is 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 acid 

 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.f Some trees, also, of the exogenous class, as the 

 Ulmus Americana, or common elm of this country, not only flour- 

 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, on 

 the thinly soil-clad surface, and near the edge of a broad calca- 



* Principles, page S. t Roget, page 39, et seq. 



