174 ü. H. Scott. 



from forms (perhaps such as Lijcopodites) which have alwaj^s been 

 herbaceous, rather than that they are the reduced descendants of 

 arborescent Lepidodendreae. It is possible, however, that the Triassic 

 genus PJeuromcia may represent a link between the latter group and 

 the recent Isoctes, which, of all the living Lycopods, appears to have 

 most in common with the Lepidodendreae. 



Other points relating to the affinities of Lycopodiales will best 

 be considered as a part of the broader question of the relations of 

 Lycopsida in general. 



The Systematic Position of Lycopsida. 



The position of the Lycopsida, Avhich we provisionally accepted 

 as a main natural division of Vascular Plants, requires some further 

 consideration now that we have dealt with the various classes com- 

 prised in it, so far as our present subject demands. 



Do the classes thus grouped together really form a natural asso- 

 ciation, more nearly related among themselves than to out-lying 

 families of plants? So far as the Sphenophyllales and Equisetales 

 are concerned, the affinities are clear and undoubted and have been 

 sufficiently discussed above. We have also found reason to believe 

 that, in a different direction, the Sphenophyllales show an affinity 

 with the recent Psilotales. It is unfortunate that we have as yet no 

 certain knowledge of the geological history of the Psilotales them- 

 selves; it is not to be supposed that they sprang from the Spheno- 

 phyllales as actually known to us, but rather that the two groups 

 had a common origin. The same remark applies to the Equisetales, 

 which though nearer to the Spheuophyllaceous type, cannot have been 

 derived from any of the specialized forms of which alone the remains 

 have come down to us. The Sphenophyllales as represented in the 

 Carboniferous Flora are best regarded as the last, highly modified, 

 members of an ancient synthetic stock which in still earlier times 

 appears to have had genetic relations to various other Pteridophytic 

 phyla. The Devonian Pseudohornia, though at present placed in a 

 class of its own, may well have belonged to the same main stock 

 with the Sphenophyllales. 



The most difficult question is that of the relation of the Lyco- 

 podiales to this phylum. Anatomically an affinity seems indicated, 

 for the simpler protostelic Lycopods agree very nearly with the 

 Sphenophyllaceous type of stem-structure as represented in Clieirostrohus. 

 The verticillate arrangement of the appendages and their vascular 

 strands scarcely causes any difficulty, for it frequently occurs among 

 Lycopods, though probably not in the form of superposed whorls. 

 In the prevailing simple structure both of the leaf and of the repro- 



