XIX] MIADESMIA 275 



enclosing membrane in contrast to the thick coat of a spore 

 which is destined to be shed. The peculiar slit-like form of 

 the micropyle is a distinguishing feature, but this may be 

 readily explained as a convenient form in the case of a radially 

 elongated sporangium. The absence of an embryo, though a 

 distinguishing feature of Lepidocarpon, cannot be held to be 

 a serious obstacle to the use of the term seed ; in recent Cycads 

 the embryo, as Scott points out, may not begin to develope 

 until the seed has been shed. It is possible that the seeds of 

 Lepidocarpon were not pollinated on the parent plant. 



The lesson which this extinct type teaches, is that certain 

 Lycopodiaceous plants of the Palaeozoic era had reached an 

 important stage in the evolution of a seed. The morphological 

 essentials of true seeds had been acquired ; but we do not know 

 the biological conditions under which pollination and fertilisa- 

 tion were effected. Another point of considerable interest is 

 the value of this discovery as an argument in favour of the 

 view that some Gymnosperms are derived from Lycopod an- 

 cestors. Leaving the general question until later, it may 

 at any rate be stated that in Lepidocarpon we have a demon- 

 stration of the fact that the Lycopodiales were not always 

 distinguished from Gymnosperms by the absence of seeds. 

 There are certain features in Lepidocarpon shared by the seeds 

 of Araucarieae^ which may well mean something more than 

 mere parallel development in two distinct phyla of the plant- 

 kingdom^. 



ii. Miadesmia. 



In 1894 Prof Bertrand' published an account of certain 

 fragments of petrified leaves and twigs of a small herbaceous 

 Lycopodiaceous plant, under the name Miadesmia membranacea, 

 which he discovered in English material in association with 

 Lepidodendron Harcourtii. Subsequently Scott recognised 

 the megasporophylls of the same plant, and microsporophylls 

 have also been discovered. The most complete account of 



1 Seward and Ford (06). ^ For a contrary opinion, see Scott (09) p. 656. 

 » Bertrand, E. (94). 



