790 PROFESSOR A. ANSTRUTHER LAWSON ON 



fcive organs were confined to no particular region. The antheridia were compara- 

 tively large structures, and were found variously distributed over the surface. The 

 archegonia, on the other hand, were quite small and very numerous. This maybe 

 observed in figs. 3 and 6. In this respect Tmesipteris does not show a feature 

 which is characteristic of Lycopodium, where the reproductive sexual organs are 

 limited in their distribution. 



So, taking these main features of the prothallus of Tmesipteris into account, there 

 appears to be very little resemblance to other known Pteridophytes. Its saprophytic 

 habit and subterranean habitat do recall Lycopodium, but structually there is no 

 real resemblance. On the other hand — with the probable exception of the general 

 form of the archegonia and antheridia — there is not the remotest suggestion of 

 Equisetum, which, of course, is a free-living, chlorophyll-bearing prothallus growing 

 upon the surface of the soil. If one may draw conclusions from these few specimens, 

 which form the basis of this study, it would seem that we have in the Psilotales a 

 type of prothallus that is not closely related to any other existing Pteridophytes ; and 

 this lends support to the more recent ideas that their relationships to the Lycopodiales 

 on the one hand, and the Equisetales on the other, are very remote. The only other 

 alternative would be a close relationship to the Sphenophyllales , which has already 

 been suggested by both Scott and Bower. 



The Antheridia. 



All of the specimens found — with one exception — bore antheridia. While all of 

 the stages in the development of these structures were not found, sufficient material 

 was obtained to make a considerable study of them. In the first place, the antheridia 

 seemed not to be confined to any particular region of the prothallus. They were 

 found at both ends, in the middle and on both sides. Compared with the archegonia, 

 they were very large. They grow out from the surface as large, almost spherical, 

 structures. I do not know of any Pteridophyte that has larger antheridia. The 

 distributing of the antheridia over the surface of the prothallus is shown in figs. 

 2 and 3. These figures also show the relative size of the two kinds of reproductive 

 organs. In none of the cases examined were there archegonia found on the prothallus 

 without being accompanied with antheridia. The antheridia and archegonia were 

 nearly always found in close proximity to one another. 



The antheridia are almost spherical in form, and extend out quite conspicuously 

 from 'the surface of the prothallus as rounded protuberances. They are quite 

 evidently superficial structures, and in this respect stand in contrast to Lycopodium 

 and Equisetum and also to the description given by Lang (1904) of the supposed 

 prothallus of Psilotum, types in which the mature antheridium comes to lie below 

 the surface. As shown in figs. 3, 7, 8, 9, 10, and 11, the antheridium here in 

 Tmespiteris has a distinct character of its own, both in size and surface position. 



