4 o6 SPHENOPHYLLALES. A. SPHENOPHYLLEAE 



phylls. ] These were arranged in whorls of twelve, and were superposed : 

 each consisted of three sterile lobes palmately divided, and it bore upon 

 its upper surface, and inserted close to its base three sporangiophores ; 

 each of these was provided with four long pendent sporangia attached to 

 its peltate distal end (Fig. 223). So far as the vascular connections are 

 a guide, it may be concluded that the sporangiophores are appendages 

 of the branched sporophyll, and especially of its middle 

 segment, since a vascular strand supplying them originates 

 from the bundle which runs into the middle segment of 

 the sporophyll. This strand divides then into three, 

 and one branch enters each of the sporangiophores 

 (Fig. 224). Thus, as Scott himself points out, 2 the 

 course of the vascular bundles supplying the sporangio- 

 phores and bracts is essentially the same in Spheno- 

 phyiium and Cheirostrabus, though necessarily more 

 complex in the latter. 



FlG. 222. 



There can be little doubt of the fundamental 



Forked sporophyll of 



sphenophyiium majus, correspondence of the various types above described : 



bearing sporangiophore. ..,'.. , 



(After Kidston.) they all coincide in the presence of spore-producing 



parts subtended by sterile bracts arranged in whorls : 

 and notwithstanding their differences in number, and in the number of 

 sporangia which they individually bear, it is safe to conclude that the 

 sporangiophores are homologous throughout the series. Their similarity of 

 general structure to the sporangiophores of the Equisetales is most clearly 

 seen in Sphenophyiium majus ^ or in greatly elongated form in Cheirostrobus : 

 considering this in conjunction with their correspondence in function, there 

 is reason also to recognise a distinct relation to the sporangiophores of 

 the Equisetales. In point of position there is the difference of their being 

 leaf-borne, as against the axial insertion of the Equisetales ; in fact the 

 relation to the leaf is similar to that often seen in them, but closer. 

 The conclusion seems inevitable that the sporangiophore in these two 

 phyla is a member of similar morphological rank, though it may in both 

 phyla show some variety in its exact position. 



And here it will not be inapposite to point out in support of this view 

 some features of structural similarity which exist between the Equisetales and 

 the Sphenophyllales. They will be best illustrated in brief by the juxta- 

 position of Scott's two figures (compare Fig. 217 with Fig. 225). The 

 former shows the transverse section of the ancient S. insigne from 

 Burntisland, which differs from the later Sphenophylls in having a canal 

 marking the position of the protoxylem at each angle of the primary wood ; 

 also in having continuous medullary rays in the secondary wood, and 

 scalariform tracheides in place of those with numerous bordered pits. 



1 A second specimen, belonging also to Mr. Kidston, to whom the original discovery 

 was due, shows only eleven protoxylems. 

 2 Z.r., p. 113. 



