OBSERVATIONS OF BELGRAND. 
229 
off, and secondly, that the roots of trees penetrate and choke 
up the fissures in the rocks, so as to impede the passage of 
water through channels which nature has provided for its 
descent to lower strata. 
As to the first of these, we may appeal to familiar facts 
within the personal knowledge of every man acquainted with 
the operations of sylvan nature. I have before me a letter 
from an acute and experienced observer, containing this para¬ 
graph : “ I think that rain water does not ever, except in very 
trifling quantities, flow over the leaves in the woods in sum¬ 
mer or autumn. Water runs over them only in the spring, 
when they are pressed down smoothly and compactly, a state 
in which they remain only until they are dry, when shrink¬ 
age and the action of the wind soon roughen the surface so as 
effectually to stop, by absorption, all flow of water.” I have 
observed that when a sudden frost succeeds a thaw at the close 
of the winter after the snow has principally disappeared, the 
water in and between the layers of leaves sometimes freezes 
into a solid crust, which allows the flow of water over it. But 
this occurs only in depressions and on a very small scale ; and 
the ice thus formed is so soon dissolved that no sensible effect 
is produced on the escape of water from the general surface. 
As to the influence of roots upon drainage, I believe there 
is no doubt that they, independently of their action as absorb¬ 
ents, mechanically promote it. Not only does the water of 
the soil follow them downward,* but their swelling growth 
powerfully tends to enlarge the crevices of rock into which 
they enter; and as the fissures in rocks are longitudinal, not 
mere circular orifices, every line of additional width gained by 
the growth of roots within them increases the area of the crev- 
* “ The roots of vegetables,” says D’H6ricourt, “ perform the office of 
a perpendicular drainage analogous to that which has been practised with 
success in Holland and in some parts of the British Islands. This system 
consists in driving down three or four thousand stakes upon a hectare ; 
the rain water filters down along the stakes, and, in certain cases, as 
favorable results are obtained by this method as by horizontal drains.”— 
Annales Forestidres , 1857, p. 812. 
