SPHENOPHYLLEAE 107 



together by a network of elevated ridges or wings 

 (see Fig. 41, C). 



The above description, based on the Sphenophyllum 

 Dawsoni of Williamson, is now known to hold good, in 

 all essential points, for Sphenophyllum cuneifolium, with 

 which, indeed, M. Zeiller, to whom we are indebted for 

 a most minute comparison of the two cones, thinks it 

 identical ; this conclusion is probably correct as regards 

 the larger form of 5. Dawsoni. Several species, in 

 addition to 5. cuneifolium, were examined by M. Zeiller, 

 and in these also he was able to show that the sporangia 

 were borne on pedicels, arising from the upper surface 

 of the bracts. 



So many specimens of S. Dawsoni, all showing 

 spores of the same kind, have now been investigated 

 that there is little doubt that these cones were homo- 

 sporous. A specimen described many years ago by 

 M. Renault, and supposed to show heterospory, is 

 now admitted to have been wrongly interpreted ; the 

 structure which was formerly regarded as a megaspore 

 is in reality nothing but a fragment of tissue, probably 

 forming part of the wall of a sporangium. 



The occurrence of spores of somewhat different 

 dimensions in adjacent sporangia (averaging .083 mm. 

 in one sporangium, and .106 mm. in another), those of 

 the larger size being accompanied by minute, pre- 

 sumably abortive spores, has recently been interpreted 

 as a possible indication of incipient heterospory. 1 



3. Bowmanites Romeri, Sphenophyllum fertile, and 

 ,S. majus. — About twelve years ago the investigations of 



1 Thoday, New Phytologist, vol. v., April 1906. 



