THE CLUB-MOSSES 181 



greater importance of the vascular supply de- 

 manded by the larger leaves of that class. 



In some species of Sigillaria the vascular strand 

 forked in passing through the cortex, and here 

 we find two parallel strands in the leaf the only 

 instance among Lycopods. 



The leaves are often very well preserved, and 

 it has been found that their stomata were placed 

 in two furrows on the lower surface a pro- 

 tected position which recalls the arrangements 

 found at the present day in plants of dry climates; 

 Lepidodendrese certainly did not grow under such 

 conditions, but a similar protection against ex- 

 cessive transpiration is found in the plants of 

 salt-marshes, and this may be a more probable 

 explanation here. 



We have called the underground organs "roots" 

 and "rootlets," because these words are intelli- 

 gible and no doubt are applicable so far as func- 

 tion is concerned. The structure, however, was 

 not very root-like; the main roots had a structure 

 like that of a stem, while the rootlets had the same 

 kind of vascular system which we noticed in the 

 roots of Isoetes a single strand of wood and 

 bast, more suggestive of a leaf than of a root. 

 There are also some curious complications in the 

 structure of the rootlets, in the way of vascular 

 strands branching off into the cortex, forming a 

 special apparatus for the absorption of water. 



