CLUB-MOSSES, 107 
Selaginella, which under the name of creeping moss is used 
to adorn the soil of our hot-houses in the form of a thick 
carpet. The largest clwb-mosses of the present day are found 
in the Sunda Islands, where their stalks rise to the height 
of twenty-five feet, and attain half a foot in thickness. 
But in the primary and secondary periods even larger trees 
of this kind were widely distributed, the most ancient of 
which probably were the progenitors of the pines 
(Liycopodites). The most important dimensions were, how- 
ever, attained by the class of scale trees (Lepidodendresee), 
and by the seal trees (Sigillarieze). These two orders, with 
a few species, appear in the Devonian period, but do not 
attain their immense and astonishing development until the 
Carboniferous period, and become extinct towards the end 
of it, or in the Permian period directly following upon it. 
The scale trees, or Lepidodendrez, were probably more 
closely related to club-mosses than to Sigillariez, They 
grew into splendid, straight, unbranching trunks which 
divided at the top into numerous forked branches. They 
bore a large crown of scaly leaves, and like the trunk were 
marked in elegant spiral lines by the scars left at the base 
of the leaf stalks which had fallen off We know of scale- 
marked trees from forty to sixty feet in length, and from 
twelve to fifteen feet in diameter at the root. Some trunks 
are said to be even more than a hundred feet in length. In 
the coal are found still larger accumulations of the no less 
highly developed but more slender trunks of the remarkable 
seal trees, Sigillarieze, which in many places form the princi- 
pal part of coalseams. Their roots were formerly described 
as quite a distinct vegetable form (under the name of 
Stigmaria). The Sigillarieze are in many respects very like 
