XIl] SPHENOPHYLLUM 15 



in the absence of proof. The designation sporangiophore is no 

 doubt preferable to that of ventral lobe as it carries with it 

 no admission of particular morphological value ; as a further 

 concession to a non-committal attitude we may provisionally at 

 least regard a sporangiophore as an organ sui generis " and not 

 the result of modification of any other part'." 



The view put forward by Prof. Lignier^ that the Spheno- 

 phy Hales are descendants of primitive ferns is not convincing, 

 and his comparison of Sphenophyllum with Archaeopteris lacks 

 force in view of our ignorance as to the nature of the reproductive 

 organs of the latter genus. That the Sphenophyllales are 

 connected with the Equisetales and with the Psilotales by 

 important morphological features is clear ; but the comparison 

 between the sporophylls of the extinct genera with those of the 

 existing genus Tmesipteris, though helpful and possibly based 

 on true homology, cannot be considered as settling the morpho- 

 logical value of the sporangiophores of Sphenophyllum and 

 Cheirostrobus. 



I do not propose to discuss at length the different views in 

 regard to the morphological nature of the sporangiophore of 

 Sphenophyllum. The comparison, which we owe in the first 

 instance to Scott, with the synangium of the Psilotales with its 

 short stalk, though not accepted by Lignier as a comparison 

 based on true homology, is one which appeals to many botanists 

 and is probably the best so far suggested. The further question, 

 whether these sporangiophores are to be called foliar or axial 

 structures is one which has been answered by several authors, 

 but it is improbable that we shall soon arrive at a decision likely 

 to be accepted as final. Discussions of this kind tend to assume 

 an exaggerated importance and frequently carry with them the 

 implication that every appendage of the nature of a sporangio- 

 phore can be labelled either shoot or leaf. We treat the 

 question from an academic standpoint and run a risk of 

 ignoring the fact that the conception of stem and leaf is based 

 on morphological characteristics, which have been evolved as 

 the result of gradual differentiation of parts of one originally 



1 Bower (08) p. 426. "" Lignier (03) ; (08). 



