616 
THE PRINCIPLES OF BOTANY. 
In the economy of man they perform hut an insignificant 
part, but in the economy of nature how vast an end !” — 
Vegetable Kingdom. 
Not a damp wall or floor, barren rock, mountain top, 
or spongy morass, but may be the location of some species 
of moss which from its curious structure can hardly fail if 
examined to interest the most incurious. 
Once they were employed in medicine, but they are now 
entirely disused. In the shape of peat, which is mostly 
composed of different species of Sphagnum , they form not 
only the dwelling, but the fuel of many of the poorer in- 
habitants, especially of Scotland and Ireland ; and there is 
reason to think that much of the coal which has been so 
abundantly supplied to this country is due to mineralised 
masses of mosses mixed with other forms of vegetation, 
especially gigantic Horsetails and Club-mosses. The Club- 
moss — Lycopodium of our flora — is interesting on account of 
its curious sporules. These, as collected from L. clavatum 
and L. selago, form a highly inflammable powder called 
“ vegetable brimstone,” which is used for making fireworks, 
and employed by the pharmacien for dusting pills. Sir W. 
Hooker says that one species — L. rubrum , by him called L. 
catharticum — acts vehemently as a purgative, and has been 
administered extensively in Spanish America in cases of 
elephantiasis. The sporules may also be used for dusting 
excorated surfaces, and there is reason to think that in this 
way it may be of great value in preventing those abrasions 
from harness, &c., to which horses are so liable. 
Ferns. — Although without flower, yet from the interesting 
forms of their leaves — fronds — form a highly favorite group 
of plants, so much so, indeed, that numerous and highly 
valuable works have been devoted to them alone. They are 
variously grouped, but for our present purpose it will be 
sufficient to mention that some forms are of sufficient height 
and size to be denominated tree-ferns, whilst others are so 
diminutive as at first to be scarcely distinguishable from the 
lowly moss. 
Of the tree-ferns, some of them have trunks as much as 
forty feet in height, a careful examination of the boles of 
which, after all, lead to the supposition that this solid struc- 
ture is composed of the bases of the leaves in union, and it 
will be observed that this stem is marked all over with escars 
of the decayed leaves or fronds, i. e. the bases of their stipes. 
Arborescent ferns are never branched, though they may 
be occasionally dichotomous from abnormal growth or 
accident. The largest tree-fern, like the smallest of the 
