MOSSES, 31 
firm a hold of the earth, in proportion to their size, 
as the roots of many trees. In some cases they 
consist of small thread-like fibres, or long creeping 
underground stems; while in others they are 
aérial, like those of orchids, being developed in the 
form of a thick silky down of a pale brown colour, 
imbedded among the leaves close to the stem. 
This last variety of root is to be seen chiefly in 
species that grow in moist or watery places, where 
they act as sponges to attract and preserve the 
humidity of the plants, when the moisture around 
them is dried up. In connexion with their roots 
we observe a striking provision of Nature for the 
welfare of mosses in unfavourable circumstances. 
As the most delicate fibres hardly penetrate be- 
yond the surface of the soil, which in dry 
sultry weather speedily parts with its moisture, 
the mosses would perish were they entirely de- 
pendent for their nourishment upon their roots. 
But every part of them, and especially the leaves, 
is endowed, to a remarkable degree, with the 
power of imbibing the faintest moisture from the 
air, and reviving, even when apparently withered 
and dead, on the recurrence of a shower of rain. 
The roots therefore, in most instances, serve only 
to attach the plant to its growing-place, the func- 
tions of nutrition being performed indiscriminately 
by its whole surface. 
