406 SPHENOPHYLLUM. [CH. 



A further variation in the structure of the strobili is 

 illustrated by some specimens of S. trichomatosum Stur, 

 described by Kidston', from the Coal-Measures of Barnsley. 

 Each whorl of bracts bears a single series of oval sporangia 

 which appear to be sessile on the basal portion of the whorl. 

 It is possible that delicate sporangiophores may have been 

 present, but in the imperfect examples in Kidston's collection^ 

 the sporangia present the appearance of being seated directly 

 on the surface of the bracts. As the specimens do not show 

 any internal structure, it would be unwise to lay too much 

 stress on the apparent absence of the characteristic sporang- 

 iophores. In any case, Kidston's cones afford an illustration of 

 the occurrence of a single series of sporangia in each whorl, 

 instead of the pluriseriate manner of occurrence in some other 

 species. 



The statement is occasionally met with that some Spheno- 

 phyllum cones possessed two kinds of spores, but we are still 

 in want of satisfactory evidence that this was really the case. 

 Renault has described an imperfect specimen, which he con- 

 siders points to the heterosporous nature of a Sphenophyllum 

 cone, but Zeiller and Williamson and Scott have expressed 

 doubts as to the correctness of Renault's conclusions. While 

 admitting the possibility of undoubted heterosporous strobili 

 being discovered, we are not in a position to refer to Spheno- 

 phyllum as having borne strobili containing two kinds of 

 spores ^ 



[The following are some of the specimens in the Williamson Cabinet 

 which illustrate the structure of Sphenophyllum : — 



»S'. plurifoliatum. 874, 882, 884, 893, 894, 897, 899, 901, 903, 908, 1893. 



S. insigne. 910, 914, 919, 921, 922, 924, 926, 1420, 1898. 



Sphenophyllostachys. 1049a— 1049o, 1898.] 



1 Kidston (90). 



^ I am indebted to my friend Mr Kidston for an opportunity of examining 

 these specimens. 



3 Vide Eenault (77), (96), p. 158. Zeiller (93), p. 34. WUliamson and 

 Scott (94), p. 942. 



