THE PENNSYLVANIAN PERIOD. 



599 



The trunks of lepidodendrons were erect and branched dichoto- 

 mously at a great height, some having been found 100 feet in length, 

 which is probably not the maximum. The leaves were linear or needle- 

 shaped, ranging up to six or seven inches in length, and were set densely 

 on the branches. The breathing pores were confined to the walls 

 of two very deep furrows on the underside of the leaves. Besides a 

 protecting epidermis, there were thick- walled cells within, as in the 

 modern pine, and the mesophyll was loose without palisades, facts 

 of interest as bearing on climatic or other conditions to be discussed 

 later. The manner of reproduction is a point of peculiar interest, 



Fig. 280. — Leaf markings of a lepidoden- 

 dron, Lycopodites welthermianum, St. 



Fig. 281. — Leaf markings of 

 sigillarian. 



for in some cases the fruit seems to have taken on the characteristics 

 of seeds rather than spores, making the development of the lycopods 

 fall into analogy with that of the fern group, in passing from the spore- 

 bearing to the seed-bearing habit. It is not yet known whether any 

 of these seed-bearing lycopods developed into permanent gymno- 

 spermous types or not. One form of the fruit was distinctly winged, 

 and other forms showed adaptation to transportation by wind. Over 

 100 species have been described. 



The sigillarians differed from the lepidodendrons in being almost 

 entirely unbranched. They were perhaps the largest of the Carbon- 



