SIGILLARIOSTROBUS 237 



As we shall see later on, there is strong evidence for 

 tracing the origin of the Cycadales from quite a different 

 Cryptogamic phylum, namely that of the Ferns. 



The question of a possible affinity between the 

 Palaeozoic Lycopods generally and certain of the 

 Coniferae, an hypothesis advocated by some modern 

 writers, will be considered in the concluding chapter. 



II. Stigmaria 



1. Habit and External Characters. — The subject of 

 the roots or other subterranean organs, both of Lepido- 

 dendron and Sigillaria, has been postponed so far, 

 because it presents considerable difficulty, and we are 

 not even now in a position to distinguish the roots of 

 the one genus from those of the other. 1 Yet Stigmaria 

 ficoides, which includes most of the specimens in question, 

 is the very commonest of all fossils in the English 

 Coal-measures, and other strata of similar horizon, and 

 its outward appearance is familiar to every one who 

 has paid the least attention to fossil remains. The 

 Stigmariae, which are ordinarily preserved as structure- 

 less casts, are long, more or less cylindrical or slowly 

 tapering bodies, varying in diameter from an inch or 

 so up to more than two feet. The surface is marked 

 all over with quincuncially arranged circular scars. 

 Each scar is depressed, with a raised margin ; within 

 the scar is a second, much smaller circle, in the centre 

 of which a raised point can be detected in good 

 specimens (Fig. 97). The scars mark the insertion of 



1 The morphological character of these organs is considered below, 

 p. 259. The word "root" is used here in a physiological sense. 



