GENERAL RESULTS— SPHENOPSIDA 621 



the stem of the Lower Carboniferous Protocalamites 

 (P- 37)- 1 



The evidence from the fructifications strongly 

 supports the affinity between Sphenophyllales and 

 Equisetales, though the detailed comparison presents 

 some difficulties. The minute structure of the sporangia 

 is strikingly similar in the two classes, and the 

 resemblance extends to the sporangiophores. Those of 

 Cheirostrobus in particular, which have four sporangia, 

 are almost identical with those of Calamostachys (pp. 

 54 and 116). Where the number of sporangia is 

 smaller the resemblance to the Equisetal type becomes 

 less evident. 



Throughout the Sphenophyllales the sporangio- 

 phores occupy the position of ventral lobes of the 

 sporophyll ; in one species, 5. fertile (p. 1 1 1 ), the dorsal 

 lobes are also enlisted for the same service. This 

 latter case is of special interest, because the dorsal and 

 ventral lobes are on an equal footing, both being 

 organised in the same way ; the segments of each lobe 

 constitute typical bisporangiate sporangiophores. I 

 incline to regard this form as a secondary modification 

 rather than a primitive type, partly because the case 

 is at present altogether exceptional and of no special 

 antiquity, and partly because the dorsiventral arrange- 

 ment seems best explained on the supposition that 

 the dorsal lobes were originally sterile and protective 



1 Mr. Gwynne-Vaughan has suggested that the lateral xylem -strands in 

 the recent Equisetum may represent the centripetal wood. Their posi- 

 tion, however, is very different from that of the centripetal wood in 

 Protocalamites, and the matter requires further investigation. See D. T. 

 Gwynne-Vaughan, " Remarks upon the Nature of the Stele of Equisetum," 

 Ann. of Bot. vol. xv. 1901, p. 774. 



