90 Proceedings of the Royal Physical Society. 



Lepidodendra, in tlieir fructification, approach most closely 

 to Selaginella, the cones of which, as well as those of L&pido- 

 deiidron, contain both micro- and macrospores, the latter 

 usually occupying the lower, and the former the upper 

 sporangia.^ 



Sigillaria, on the other hand, has been referred to Isoetes ; ^ 

 but it appears to us that a more satisfactory position is that 

 accorded it by Zeiller, viz., an intermediate place between 

 Lepidodendron and Isoetes.^ To Isoetes, Sigillaria appears to 

 be related by the arrangement of the sporangia, and perhaps 

 through its mode of disseminating the spores; to Lepido- 

 dendron by the structure of the leaf-scars and the internal 

 anatomy of its stem.* 



The gigantic size of the macrospores of fossil Lycopods has 

 led several botanists to regard them as sporangia. When 

 examined as transparent objects, they are found to be com- 

 posed of a single cell, whose wall seems to consist of two 

 layers. In many cases the outer layer of the spore wall (the 

 exosporium) separates from the inner layer (the endosporium), 

 and in this condition their microscopical examination is easily 

 accomplished. 



Had these fossils ever possessed a cellular structure, traces 

 of it would still be preserved ; for associated with the macro- 

 spores are numerous films of epidermal tissue, showing most 

 exquisitely preserved cellular structure. 



1 In some species of Selaginella the micro- and macrosporangia are mixed. 



2 Goldenberg, I.e., Heft i., p. 24. 



^ Itenaiilt thinks that certain Sigillarim are Lycopodiaceous, others Cyca- 

 daceous {see Sur les Fructifications des Sigillaires. Comptes Rendus des 

 Seances de I'Acad. d. Sc, 7th Dec. 1885). This paper has been reviewed by 

 Weiss (Sitzungs-Bericht der Gesellschaft naturforschender Freimde zu Berlin, 

 No. 2, 16th February 1886), who is of opinion that the present knowledge of 

 the fructification of Sigillaria does not warrant the adoption of this view. 



4 Zeiller, I.e., p. 278. 



Note. — Though not immediately connected with the spores specially 

 engaging our attention, it may be interesting to refer to a group of these 

 organisms which Sir 0. W, Dawson described in the Proc. of the American 

 Assoc, for Advancement of Science, 1883, These he believes to be Rhizo- 

 carpian, and has proposed for them the name of Protosalvinia, on account of 

 the resemblance of the fossil spore cases to those of the genus Salvinia. See 

 also Bui. Chicago Acad. Sc, voh i., No. IX., p. 105, 1886, On Rhizocarps 

 in the Erian Period in America. 



