LYCOPODITEAE 265 



S. elongatus may represent a less advanced condition, 

 but it must be remembered that Miadesmia, a con- 

 temporary or older genus, went far beyond any other 

 known herbaceous Lycopods in the specialisation of 

 its megasporangia. Nothing certain is known, as yet, 

 of any homosporous type of Lycopoditeae. If, however, 

 the Rhaetic plant Naiadita is rightly referred to 

 Lycopodiaceae, we may have an example from the 

 Mesozoic, for the spores, which are found grouped in 

 tetrads in the sporangia, have a diameter of 80 /x, 

 and only one kind has been observed. 1 



Conclusion 



We have now completed our survey of the Palaeozoic 

 Lycopods, a group remarkable for the high develop- 

 ment which they attained, both in vegetative and 

 reproductive characters. The anatomical complexity 

 of the Lepidodendreae was clearly correlated with the 

 arboreal habit, which was then so prevalent. Apart 

 from this, the structure, so far as the primary tissues are 

 concerned, was on the whole of a simple type — simpler 

 than that of the majority of recent Lycopods. The 

 remarkable morphology of the subterranean organs 

 (Stigmaria) may possibly indicate a somewhat primitive 

 stage in the differentiation of root and shoot, though 

 it may also be interpreted as a special modification, 

 due to the peculiar conditions of growth. The 

 morphology of the vegetative organs, even in the 

 highly organised Lepidodendreae, is not in itself 



1 See Miss J. B. J. Sollas, " Naiadita lanceolata," Quart. Journ. Geol. 

 Soc. vol. Ivii. 1901, p. 307. 



