1 20 
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appears to be the real heterosporous form corresponding to Lyco- 
podium , and probably the fossil heterosporous Lycopodinous forms 
belong really to the Selaginelleae. 
Although this position of Isoe'tes has met with general acceptance, 
yet it is a question whether it really corresponds to its true affinities. 
Goebel himself says 1 , £ The groups which have been brought together 
under the name of Ligulatae have scarcely anything in common but 
the presence of a ligule, and it would be better perhaps to make 
separate divisions of them/ But if there is little in common between 
the Isoeteae and the Selaginelleae, there must be still less in common 
between Isoe'tes and the Lycopodiaceae. The question at issue is, 
therefore, not merely whether the Selaginelleae and the Isoeteae 
should be separated, but whether Isoe'tes really belongs to the 
Lycopodinae at all. This raises the further question; if Isoe'tes 
be removed from the Lycopodinae, with what group of Vascular 
Cryptogams shall it be associated? It is the object of the present 
note to endeavour to answer these questions. 
Taking first the question of the affinity of Isoe'tes with the Lyco- 
podinae, it becomes at once apparent that there are many important 
differences between them. The general characteristic of the sporo- 
phyte of the Lycopodinae is that the stem is slender and much 
branched, the leaves being small and numerous ; in Isoe'tes, on the 
contrary, the stem is short, thick, and unbranched, and the leaves 
are relatively large. It is true that in habit Phylloglossum more nearly 
resembles Isoe'tes than it does the other Lycopodinae; but even 
here 2 there is a branching of the stem, at least in the sporangiferous 
forms, in connexion with the formation of the tubers. Again, the 
sporangia of the typical Lycopodinae are borne on sporophylls which 
are confined to special branches ; and in the majority the sporophylls 
differ from the foliage-leaves and are aggregated together into cones 
on special shoots : in Isoe'tes all the foliage-leaves are sporangiferous. 
Further, so far as the embryogeny of the sporophyte is known in 
the Lycopodinae, that is, in the case of Lycopodium and Selaginella, 
there is a suspensor but no primary root ; whereas in Isoe'tes there is 
a primary root but no suspensor. As regards the gametophyte, the 
mode of germination of the microspores is much the same in Isoe'tes 
3 Outlines, p. 196. 
2 Bower, On the development and morphology of Phylloglossum Drummondii , 
Phil. Trans. II, 1885. 
