The Present Position of Palaeozoic. Botany. 



171 



intermediate in size between the microspores and megaspores of a 

 Lepidostrohus, and are furnished with a very characteristic wing, 

 which probably aided in dispersal. As only one kind of spore has 

 been observed it is possible that Spencerifes was homosporous, though 

 the number of specimens investigated is not sufficient to place this 

 conclusion beyond doubt. Vegetative stems, agreeing very closely in 

 structure with the axis of Spencerites, are known, and suggest a 

 possible relation to Bothrodendron. 



The discovery of the hetero- 

 sporous cones of SigiJJaria (SigiUarw- 

 strobus) was important as proving 

 the Cryptogamic nature of these 

 plants, long regarded by Brong- 

 n i a r t and his followers as Gymno- 

 sperms. Structurally, Sigillariosfro- 

 hiis appears to present no very 

 essential distinctions from the Lepi- 

 dostrobm type. 



The most interesting, however, 

 of the Palaeozoic Lj^copodineous 

 fructifications are those which show 

 a near approach to the production 

 of seeds. At present two genera 

 are known in which the mega- 

 sporangium assumed a seed-like 

 character — Lepidocarpon and 3Iia- 

 desmia. In Lepidocarpon (Scott, 

 1901) the anatomy and morphology 

 of the megasporangiate cone, in its 

 young condition, are in all respects 

 those of an ordinary Lepidostrohus. 

 The megasporangia are attached, 



in the usual manner, to the upper surface of the sporophylls, which 

 are provided with ligules, as in Lepidostrohus. The palisade-struc- 

 ture of the sporangial wall is also the same as in that genus. In 

 each megasporangium, however, only a single megaspore came to 

 perfection, filling practically the whole cavity, like an embryosac; 

 its three sister- cells can often be detected in an abortive con- 

 dition. At maturity, the megasporangium was enclosed in an inte- 

 gument (Fig. 11), springing from the upper surface of the sporophyll, 

 and forming a complete investment to the sporangium, except for a 

 narrow crevice along the top, comparable to a micropyle, but of great 

 length, corresponding to the radial elongation of the sporangium. 

 A¥ithin the one functional megaspore, a prothallus was developed, 



Fig'. 11. Lepidocarpon Lomaxi. Dia- 

 grammatic section of seed-like organ 

 cut in plane tangential to the parent 

 strohihis. sph, sporophyll ; v. b, vascu- 

 lar bundle; i, integument: m, micro- 

 pylar crevice ; sm, wall of sporangium ; 

 a, insertion of sporangium on sporo- 

 phyll; mg, membrane of megaspore or 

 embryo-sac ; p)^', prothallus filling mega- 

 spore. 



