126 STUDIES IN FOSSIL BOTANY 



other plants, and evidently much modified along 

 peculiar lines of its own. 



Selaginella, in a few species {e.g. S. spinosd), has a 

 simple and probably primitive anatomical structure, 

 but in a great majority of the forms this has become 

 much elaborated ; in a large part of the genus the 

 dimorphic foliage is another mark of specialisation. 



The genus Isoetes is clearly a reduced form, and 

 differs in so many points from the rest of the Lycopods, 

 that some doubt has even been cast on its affinity 

 with them, and it is largely by a comparison with 

 fossil types that its position has been re-established. 



The Psiloteae, as we shall see in the concluding 

 chapter, appear, in the light of our present knowledge, 

 to be remote from the true Lycopods, and rather to 

 show affinity with the Sphenophyllales. 



Broadly speaking, then, we may say that the 

 representatives of the Class now living consist of a 

 number of specialised forms, from which it is not easy 

 to form an idea of the primitive characters of the 

 common stock. The Palaeozoic Lycopods throw a new 

 and welcome light on the problem. They were not, it 

 is true, simple forms ; like so many other Cryptogams 

 of early periods, they attained in some respects a much 

 higher grade of organisation than their living repre- 

 sentatives. Yet, in the ground plan of their structure, 

 the fossil forms probably give us a better idea of the 

 essential characters of the group than any of their 

 recent allies. 



i. Habit. — We will begin with the great genusLepzdo- 

 dendron, of which more than a hundred so-called species 



