Page:Proceedings of the Royal Society of London Vol 69.djvu/365

Rh 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.

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.