142 ANCIENT PLANTS 



is suggestive of the effect that such a position has on 

 the families occupying it, however lowly they may be. 

 The simple Pteridophyte Lycopods had not only the 

 tall trunks and solid woody structure of a modern tree, 

 but also a semblance of its seeds. Whether this line 

 of development ever led on to any of the higher families 

 is still uncertain. The feeling of most specialists is that 

 it did not; but there are not wanting men who support 

 the view that the lycopod affinity evolved in time and 

 entered the ranks of the higher plants, and indeed there 

 are many points of superficial likeness between the 

 palaeozoic Lycopods and the Coniferae. Judged from 

 their internal • structure, however, the series through the 

 ferns and Pteridosperms leads much more convincingly 

 to the seed plants. 



In their roots; or rather in the underground struc- 

 tures commonly called roots, the Lepidodendrons were 

 also remarkable. Even more symmetrically than in 

 their above-ground branching, the base of their trunks 

 divided; there were four main large divisions, each of 

 which branched into two and these into two again. 

 These 'Structures were called Stigmaria, and were com- 

 mon to all species of Lepidodendron and also the group of 

 Sigillaria (see fig. 102). On these horizontally running 

 structures (well shown in the frontispiece) small append- 

 ages were borne all over their surface in great profusion, 

 which were, both in their function and microscopic struc- 

 ture, rootlets. They left circular scars of a characteristic 

 appearance on the big trunks, of which they were the 

 only appendages. These scars show clearly on the 

 fragments along the ledge to the left of the photograph. 

 The exact morphological nature of the big axes is not 

 known; their anatomy is not like that of roots, but is 

 that of a stem, yet they do not bear what practically 

 every stem, whether underground or not, has developed, 

 namely leaves, or scales representing reduced leaves. 

 Their nature has been commented on previously (p. 69), 

 and we cannot discuss the point further, but must be 



