182 THE EVOLUTION OF PLANTS 



There are many instances in Lycopods of struc- 

 tures which do not quite fall under the head of 

 root or of shoot; this may possibly be an indica- 

 tion that the group is in some respects a primi- 

 tive one, retaining some characters which date 

 from a time when the different organs of the 

 plant-body were not quite sharply differentiated. 

 None the less, the organs in question, and espe- 

 cially those of the fossils, show remarkably perfect 

 adaptation to their functions. The main "roots" 

 of the Lepidodendrese have been compared to 

 those curious organs, the leafless root-bearing 

 branches of Selaginella. 



We must now pass on to the organs of repro- 

 duction. The sporangia, as we have seen, were 

 always borne in definite cones, the general organ- 

 isation of which was, broadly speaking, on the 

 same lines as in a recent Lycopod, the genus 

 Selaginella, with its two kinds of spores, afford- 

 ing the best parallel, though far from an exact 

 one. Indeed, in some respects the analogy with 

 Isoetes is greater, only in that genus there is no 

 cone differentiated. 



There are two grades of organisation in the 

 fructifications of Lepidodendrese; on the one 

 hand, we have a typical heterosporous mode of 

 reproduction, on about the same level as that of 

 Isoetes and Selaginella in the recent Flora. On 

 the other hand, we find reproduction by seed-like 



