HISTORY OF PLANTS. 339 
srow up and cover the rock with variously coloured 
leaves, (frons). After some time wind and_ rain 
bring fine dust into the clefts of the rocks, and the 
decayed algae themselves leave a kind of covering 
stratum behind. In this earth, though sparingly 
scattered, other seeds of mosses, which chance con- 
veys thither, will germinate. ‘They spread and form 
a fine green layer, which is soon able to lodge other 
small plants in its interior. The decay of those 
mosses and smaller plants produces, by degrees, a 
thin stratum of earth, which increases with years, 
and now even allows some shrubs and trees to grow. 
iit, till finally, after a long series of years, where once 
barren rocks stood, large forests with their magnificent 
branches delight the wanderer’s eye. ‘Thus nature 
proceeds, acting by degrees, always great, constant, 
and intent on the good of the whole. In like man- 
ner, mosses correct and meliorate dry and barren 
sand. Plants peculiar to such sandy soil are almost 
all of them provided with creeping, spreading roots, 
which are very succulent, and imbibe moisture from 
the atmosphere. ke therefore render the ground 
fit for the reception of algae and mosses, and thus 
it is converted into good file soil. 
Mosses overspread the trunks and roots of trees, 
and have that peculiar property that they becfime 
very dry in warm weather, but revive through mois. 
ture. hey imbibe moisture eagerly, and retain ii 
in their interstices. ‘Vhey receive no nourishment 
from the trees, all their food they get from the at- 
mosphere. In winter they defend oe trunk against 
frost ; in wet weather against petrefaction, a nd dux 
(a) 
= mo 
