“178 THE NATURAL HISTORY OF SELBORNE, 
In some of our smaller islands in the West Indies, if I 
mistake not, there are no springs or rivers : but the people are 
supplied with that necessary element, water, merely by the 
dripping of some large tall trees, which, standing in the bosom 
of a mountain, keep their heads constantly enveloped with fogs 
and clouds, from which they dispense their kindly never-ceasing 
moisture ; and so render those districts habitable by condensa- 
tion alone. 
Trees in leaf have such a vast proportion more of surface 
than those that are naked, that, in theory, their condensations 
should greatly exceed those that are stripped of their leaves ; 
but, as the former imbibe also a great quantity of moisture, 
it is difficult to say which drip most; but this I know, that 
deciduous trees that are entwined with much ivy seem to 
distil the greatest quantity. Ivy-leaves are smooth, and thick, 
and cold, and therefore condense very fast ; and besides, ever- 
greens imbibe very little. These facts may furnish the intelli- 
gent with hints concerning what sorts of trees they should plant 
round small ponds that they would wish to be perennial; and 
show them how advantageous some trees are in preference to 
others. 
Trees perspire profusely, condense largely, and check evapo- 
ration so much that woods are always moist ; no wonder, there- 
fore, that they contribute much to pools and streams. 
That trees are great promoters of lakes and rivers appears 
from a well-known fact in North America ; for, since the woods 
and forests have been grubbed and cleared, all bodies of water 
are much diminished; so that some streams, that were very 
considerable a century ago, will not now drive a common mill. 
Besides, most woodlands, forests, and chases with us abound 
with pools and morasses ; no doubt for the reason given above. 
To a thinking mind few phenomena are more strange than 
the state of little ponds on the summits of chalk-hills, many of 
which are never dry in the most trying droughts of summer. 
