TRANSFER OF VEGETABLE LIFE. 
59 
wind and sun.* At a certain stage of growth, grass land is 
probably a more energetic radiator and condenser than even 
the forest, bnt this powerful action is exerted, in its full inten- 
sity, for a few days only,.while trees continue such functions, 
with unabated vigor, for many months in succession. Upon 
the whole, it seems quite certain, that no cultivated ground is 
as efficient in tempering climatic extremes, or in conservation 
of geographical surface and outline, as is the soil which nature 
herself has planted. 
Transfer of Vegetable Life. 
It belongs to vegetable and animal geography, which are 
almost sciences of themselves, to point out in detail what man 
has done to change the distribution of plants and of animated 
life and to revolutionize the aspect of organic nature; but 
some of the more important facts bearing on this subject may 
pertinently be introduced here. Most of the fruit trees grown 
* It is impossible to say how far the abstraction of water from the earth 
by broad-leaved field and garden plants—such as maize, the gourd family, 
the cabbage, &c.—is compensated by the condensation of dew, which some¬ 
times pours from them in a stream, by the exhalation of aqueous vapor 
from their leaves, which is directly absorbed by the ground, and by the 
shelter they afford the soil from sun and wind, thus preventing evapo¬ 
ration. American farmers often say that after the leaves of Indian corn 
are large enough to “shade the ground,” there is little danger that the 
plants will suffer from drought; but it is probable that the comparative 
security of the fields from this evil is in part due to the fact that, at this 
period of growth, the roots penetrate down to a permanently humid 
stratum of soil, and draw from it the moisture they require. Stirring the 
ground between the rows of maize with a light harrow or cultivator, in 
very dry seasons, is often recommended as a preventive of injury by 
drought. It would seem, indeed, that loosening and turning over the sur¬ 
face earth might aggravate the evil by promoting the evaporation of the 
little remaining moisture ; but the practice is founded partly on the belief 
that the hygroscopicity of the soil is increased by it to such a degree that 
it gains more by absorption than it loses by evaporation, and partly on the 
doctrine that to admit air to the rootlets, or at least to the earth near 
them, is to supply directly elements of vegetable growth. 
