10 NATURAL CONDITIONS OF PLANTS. 
however, perished till within the last two years ; 
since which time there has sprung up abundance 
of Lycopodium clavatum, and a Selaginella with 
Marchantia, which retain so constant a supply of 
moisture, that the Rhododendron now flourishes 
and flowers in perfection. This fact serves to 
explain why many plants in a state of nature 
(where the ground is completely covered with 
vegetation), succeed so much better than in the 
well-kept garden of the amateur ; the continued 
exhalation from the plants ensuring a constantly 
moist atmosphere, which is of as much use to 
vegetation as the rain. 
In some countries, as on the coast of 
Peru, rain scarcely ever falls, hut, from May, 
for six months, a thin veil of clouds covers the 
coast, from 9 a.m. to 3 p.m. Prom the first 
appearance of the cloud, the sand hills, as if 
by enchantment, assume the features of a beau- 
tiful garden. It is a well known fact, that many 
hilly countries have been rendered quite sterile, 
in consequence of the indiscriminate destruction 
of their trees, the roots of which, taking up more 
water from the deep-seated springs than the 
plants requires for their own use, distil the surplus 
through the leaves upon the ground, forming so 
many centres of fertility. “ Spare the forests, 
especially those which contain the sources of 
