CLUB-MOSSES, IO7 



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 cluh-7nosses 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 

 (Lycopodites). The most important dimensions were, how- 

 ever, attained by the class of scale trees (Lepidodendre^), 

 and by the seal trees (SigiUarieae). 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 Lepidodendrese, were probably more 

 closely related to club-mosses than to Sigillariese. 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 leng-th. In 

 the coal are found still larger accumulations of the no less 

 highly developed but more slender trunks of the remarkable 

 seal trees, Sigillariese, which in many places form the princi- 

 pal part of coal seams. Their roots were formerly described 

 as quite a distinct vegetable form (under the name of 

 Stigmaria), The SigUlariese are in many respects very like 



