212 THE EVOLUTION OF PLANTS 



class of the Sphenophylls, not very extensive ac- 

 cording to our present knowledge, but extremely 

 interesting as representing an extinct type of 

 organisation. The genus Sphenophyllum, which 

 includes nearly all the members of the class, ap- 

 pears in the Upper Devonian, extends through 

 the whole of the Carboniferous and Permian 



Fig. 24. Sphenophyttum. Fragment of stem, showing two 

 whorls of leaves. After Coemans and Kickx. 



epochs, and is lost at the beginning of the Meso- 

 zoic. There are, however, some recent plants (the 

 little "epiphytic family Psilotacese, formerly in- 

 cluded under Lycopods) which seem to have some 

 relation to the fossil group. 



The species of Sphenophyttum the only genus 

 of which we know enough to give a general de- 

 scription were slender, graceful plants, very 



