1894.] On the Fossil Plants of the Coal-Measures. 121 



logy and anatomy of the strobilus are similar to, but not identical 

 with, those of the homosporous C. Binneyana. 



The macrosporangia and microsporangia were borne in the same 

 strobilus, and in one case both kinds of sporangia were found on the 

 same sporangiophore. 



The diameter of the microspores is about 0'075 mm. ; that of the 

 macrospores is just three times as great. 



In the macrosporangia, but never in the microsporangia, numerous 

 abortive spores are constantly found. They are of variable size, 

 but are always much smaller even than the microspores of the same 

 plant. Their invariable presence in the macrosporangia, and equally 

 constant absence from the microsporangia, leave little doubt that 

 they were the abortive sister-cells of the macrospores. 



These facts appear to throw some light on the origin of the phe- 

 nomenon of heterospory in the genus Galamostachys. In 0. Binneyana 

 the abortion of certain sister-cells of the spores, involving the better 

 nutrition of the survivors, had already begun, but still took place 

 equally in all sporangia. In G. Casheana the same process, carried 

 further in certain of the sporangia, rendered possible the development 

 of specially favoured macrospores, which attained their relatively 

 large size at the expense of their neighbours, which remained rudi- 

 mentary. All analogy leads us to suppose that to these macrospores 

 the formation of a female prothallus was entrusted. In the micro - 

 sporangia no abortion appears to have taken place, and the spores 

 attained a uniform small size. 



The axis of the strobilus of G. Gasheana has a well-marked zone of 

 secondary wood, thus affording direct evidence of the occurrence of 

 secondary growth in a heterosporons Cryptogam. 



The affinities of Calamostachys are discussed at length. In neither 

 of the species in question has the strobilus been found in connexion 

 with vegetative organs. Other species however, e.g., G. Ludwtgi^ 

 were borne on undoubtedly Calamarian stems. 



The fructification of a true Galamites has been described in a pre- 

 vious memoir (Williamson, " Organisation of the Fossil Plants of 

 the Coal-Measures, Part XIV," ' Phil. Trans.,' 1888). This strobilus 

 differs from Galamostachys in the position of the sporangiophores, 

 which were approximately axillary (instead of being placed in inde- 

 pendent verticils, midway between those of the bracts), and also in 

 the anatomy of the peduncle and axis, which was identical with that 

 of the stem of a typical Galamites. To this fossil we now propose to 

 give the name of Galnmites pedunculatus. 



The position of its sporangiophores is that characteristic of Weiss's 

 genus Palceostachya. 



The only certain fructification of a Galamites thus differs consider- 



y from a Galamostachys. The differences, however, are not such 



" 



