DRAINAGE BY ROOTS OF TREES. 207 
the earth laid open to the air and sun, the moisture has been 
evaporated, and the removal of the highways and of human 
habitations from the bleak hills to the sheltered valleys, is one 
of the most agreeable among the many improvements which 
later generations have witnessed in the interior of the Northern 
States.* 
Recent observers in France affirm that evergreen trees exer- 
cise a special desiccating action on the soil, and cases are cited 
where large tracts of land lately planted with pines have been 
almost completely drained of moisture by some unknown action 
of the trees. It is argued that the alleged drainage is not due 
to the conducting power of the roots, inasmuch as the roots 
of the pine do not descend lower than those of the oak and 
other deciduous trees which produce no such effect, and it 
is suggested that the foliage of the pine continues to exhale 
through the winter a sufficient quantity of moisture to ac- 
count for the drying up of the soil. This explanation is 
improbable, and I know nothing in American experience of 
the forest which accords with the alleged facts. It is true 
that the pines, the firs, the hemlock, and all the spike-leaved 
evergreens prefer a dry soil, but it has not been observed 
that such soils become less dry after the felling of their trees. 
The cedars and other trees of allied families grow naturally in 
moist ground, and the white cedar of the Northern States, 
Thuya occidentalis, is chiefly found in swamps. The roots of 
this tree do not penetrate deeply into the earth, but are spread 
out near the surface, and of course do not carry off the waters 
of the swamp by perpendicular conduction. On the contrary, 
by their shade, the trees prevent the evaporation of the super- 
* The Tuscan poet Giusti, who had certainly had little opportunity of observ- 
ing primitive conditions of nature and of man, was aware that such must have 
been the course of things in new countries. ‘‘ You know,” says he in a let- 
ter to a friend, ‘‘ that the hills were first occupied by man, because stagnant 
waters, and afterwards continual wars, excluded men from the plains. But 
when tranquillity was established and means provided for the discharge of the 
waters, the low grounds were soon covered with human habitations.” —Lettere, 
Firenze, 1864, p. 98. 
