6 3 6 STUDIES IN FOSSIL BOTANY 



instance of a homosporous Palaeozoic Lycopod has 

 yet been discovered. Wherever the material has 

 allowed of a definite conclusion, two forms of spore, as 

 sharply differentiated as in any recent members of the 

 class, have been found. Spencerites is sometimes cited 

 as an exception, but the evidence is inconclusive, and 

 the spores are singularly unlike those of any known 

 homosporous Lycopod 1 (p. 189). The oldest known 

 genus of Lycopods, Botkrodendron, was markedly 

 heterosporous, if we may judge from the Coal-measure 

 species. Among the herbaceous as well as the 

 arborescent Lycopods, only heterosporous forms have 

 so far been detected ; in some of the former (Sela- 

 ginellites primaevus) there is an exact agreement with 

 the recent Selaginella (p. 264). 



It is impossible to doubt that homosporous Lyco- 

 pods existed in Palaeozoic times, but the prevalence of 

 higher methods of reproduction shows how far the class 

 had already advanced at the period when our fossil 

 record begins. 



Certain Lycopods, as we have seen (p. 193), went 

 beyond mere heterospory, and developed organs closely 

 analogous to true seeds. Of the two genera in which 

 seed -like organs are known, the one, Lepidocarpon, 

 clearly belonged to the Lepidodendreae, while the 

 other, Miadesmia, appears to have been a small herb- 

 aceous plant, perhaps, as Miss Benson has suggested, 



1 Professor W. H. Lang has recently traced some analogies between 

 the structure of the cone of Spencerites and that of Lycopodium cernuum. 

 These resemblances, even if fully confirmed, cannot, however, be accepted 

 as indicating affinity until the comparison rests on a much broader basis. 

 See Lang, "Preliminary Statement On the Morphology of the Cone of 

 Lycopodium cernuum and its Bearing on the Affinities of Spencerites " 

 Proc. Royal Soc. of Edinburgh, vol. xxviii. Part v. 1908. 



