206 DRAINAGE BY ROOTS OF TREES, 
growth of trees, and at the same time too retentive of moisture 
to part with it readily to the capillary attraction of the roots. 
The trees, finding abundant nutriment near the surface, and so 
sheltered against the action of the wind by each other as not 
to need the support of deep and firmly fixed stays, send their 
roots but a moderate distance downwards, and indeed often 
spread them out likea horizontal network almost on the surface 
of the ground. In the artificial wood, on the contrary, the 
spaces between the trees are greater; they are obliged to send 
their roots deeper both for mechanical support and in search 
of nutriment, and they consequently serve much more effectually 
as conduits for perpendicular drainage. 
It is only under special circumstances, however, that this 
function of the forest is so essential a conservative agent as in 
the two cases just cited. In a champaign region insufficiently 
provided with natural channels for the discharge of the waters, 
and with a subsoil which, though penetrable by the roots of 
trees, is otherwise impervious to water, it is of cardinal im- 
portance; but though trees everywhere tend to carry off the 
moisture of the superficial strata by this mode of conduction, 
yet the precise condition of soil which I have described is not 
of sufficiently frequent occurrence to have drawn much attention 
to this office of the wood. In fact, in most soils, there are coun- 
teracting influences which neutralize, more or less effectually, 
the desiccative action of roots, and in general it is as true as 
it was in Seneca’s time, that “the shadiest grounds are the 
moistest.” * 
It is always observed in the American States, that clearing 
the ground not only causes running springs to disappear, but 
dries up the stagnant pools and the spongy soils of the low 
grounds. The first roads in those States ran along the ridges, 
when practicable, because there only was the earth dry enough 
to allow of their construction, and, for the same reason, the 
cabins of the first settlers were perched upon the hills. As the 
forests have been from time to time removed, and the face of 
* SENECA, Questiones Naturales, iii, 11, 2. 
