The Affinity of Tmesipteris with the Sphenophyllales. 349 



Dr. Scott has expressed the opinion* that the Psilotese are clearly 

 very remote from the Lycopodiese, and has suggested the hypo- 

 thesis that they may have branched off from the main line of 

 Lycopod descent very far back, at a point where some of the charac- 

 ters common to the Sphenophyllales were still retained. 



If the evidence I have endeavoured to adduce here as to the charac- 

 ter of the sporophylls, and especially the nature of the synangium, as 

 a ventral leaf-lobe with its sporangia, be admitted, it will follow that 

 the relationship of Tmesipteris and Psilotum with the Sphenophyllales 

 is much closer than has generally been allowed, and possibly even 

 closer than was supposed by Dr. Scott. So, too, it will follow that 

 the Psilotese are more remote from the typical Lycopodina? than has 

 been supposed. 



Addendum Eeceived January 21, 1902. 



It will obviously be of importance to examine the sporophylls of 

 Psilotum, the only close ally of Tmesipteris, in order to see whether any 

 facts can be established which bear upon the inferences drawn from the 

 study of Tmesipteris. The supply of material available when the above 

 note was written was hardly sufficient to enable me to form a definite 

 conclusion, but I have since obtained an abundant supply of Psilotum 

 triqiidrum. Before describing the results obtained, it will be well to 

 refer to a memoir by Solms-Laubachj in which certain observations of 

 the sporophylls of Psilotum are contained. Unfortunately, the original 

 memoir has not yet been accessible to me, so that I can only judge of 

 its contents from references by Bower J and elsewhere. But Bower 

 saw nothing in the variations described inconsistent with the hypo- 

 thesis that the sporophyll is a single leaf with two lobes, and the 

 synangium merely a septate sporangium. But the character of the 

 sporophylls and their variations in Psilotum is by no means so obvious 

 as in Tmesipteris, for the leaves are greatly reduced, Psilotum friquetrum 

 being largely a xerophyte, and though the decurrent bases of the 

 leaves are distinct, the free portions are very small, and often all but 

 free from chlorophyll. Nevertheless, when we compare the sporophylls 

 of Psilotum with those of Tmesipteris, it becomes clear that they are 

 essentially similar. We find fairly numerous instances in Psilotum of 

 a second dichotomy of one branch of the first fork, or, less frequently, 

 of both branches. In the former case we find two synangia and three 

 leaf-lobes, here very minute ; in the latter case we find three synangia 

 and four leaf-lobes. When there are two synangia we find the attach- 

 ment of the one is nearer the base of the sporophyll than the other. 



* ' Studies in Fossil Botany,' p. 499. 



t ' Ann. du Jardin Bot. Buitenzorg,' 1884. 



J ' Phil. Trana.,' B, 1894, p. 544. 



