The Present Position of Palaeozoic Botany. 



153 



In one case (S. enianjinatum) there is some evidence, from Mr. 

 Hemingway's observations, that the dorsal and ventral lobes were 

 independent of one anotlier, for the sporangiophores have left their 

 own distinct scars on the axis, above the bracteal node. 



Throughout the genus SphcnophjUiim, so far as we know, the 

 spores were numerous in the sporangium, and were all of one kind. 

 The statements as to the heterospory of SpJienophjUmn, long current 

 in botanical textbooks, rested on a mistake of observation. In S. Bmv- 

 soni an appreciable difference of size in the spores has sometimes been 

 noted, but it is not likely that this had any functional significance. 



Our knowledge of the genus CJietrostrobus (Scott, 1897), from the 

 Lower Carboniferous of Scotland, is at present limited to the fructi- 

 fication, of which three specimens have been discovered. The admir- 

 able preservation of the calcified material has allowed of a minute 

 investigation of the structure. 



e~Si. 



Fig. 4. Cheirosfrohus Pettijcnrensis. Diagram of cone, the upper part in trans- 

 verse, the lower in radial section. In the transverse section, 6 sporophylls, each 

 showing 3 segments, are represented. Sp. a., section in plane of sterile segments ; 

 Sp. b., section in plane of sporangiophores ; st, laminae of sterile segments ; /', laminae 

 of sporangiophores; sm sporangia; v. b., vascular bundles supplying sporophylls; 

 Ax, axis; cy, stele. The longitudinal section shows the sporangiophores and sterile 

 segments in their relation as ventral and dorsal lobes of the sporophylls; lettering 



as before. 



