648 



GEOLOGY 



Fig. 450. Leaf markings of 

 a lepidodendron, Lycopo- 

 dites welthermianum St. 



retained. In the lepidodendrons the scars are arranged spirally 

 (Fig. 450); in the sigillarians, vertically (Fig. 451). 



The trunks of lepidodendrons were 

 tall, some having been found 100 feet 

 in length. They were erect and 

 branched dichotomously at a great 

 height. The leaves were linear or 

 needle-shaped, ranging up to six or 

 seven inches in length, and set densely 

 on the branches. Some of them were 

 heterosporous, a characteristic pointing 

 in the direction of seeds, but it is not 

 known that seed-producing plants 

 sprang from them. One form of the 

 fruit was distinctly winged, and other 

 forms showed adaptation to transporta- 

 tion by wind. More than 100 species of lepidodendrons have been 

 described. They seem to have reached their climax early in the 

 period, and nearly all had disappeared by its close. 



The sigillarians differed from the lepidodendrons in being 

 mostly without branches. They 

 were perhaps the largest of the 

 Carboniferous trees, their trunks 

 reaching six feet in diameter, and 

 100 feet or more in height. As in 

 lepidodendrons, the stems were 

 densely clothed with erect, rigid, 

 linear leaves. Like the lepidoden- 

 drons, they had a thick cork layer, 

 rarely equalled in modern trees, 

 except in the cork-oak and its allies. 

 The sigillarians exceeded the lepi- 

 dodendrons in abundance before the 



Fig. 451. Leaf markings of a 

 sigillarian. 



close of the period, but were on the wane at its close. Perhaps 

 this rather sudden decline, followed by early extinction, un- 

 connected with the changes of climate indicated by the Permian 

 glaciation, though this cannot be affirmed. 



