PRESIDENTIAL ADDRESS. 553 



would, like the stem of these plants, be exogenous.' According to the 'recapitu- 

 lation theory,' indeed, the exogenous formation of the roots in the embryo cf 

 certain Lycopods, as well as of the first root of Isoetes and the first root of the 

 Filicales, might be regarded as the retention of a more primitive character in 

 these particular organs. The roots of Stigmaria, even if exogenous, might there- 

 fore merely represent a more ancestral stage. This difference between the roots 

 of Isoetes and the rootlets of Stigmaria may, however, be more apparent than 

 real, for my colleague, Dr. Lang, has drawn my attention to the fact that there 

 appear to be in Stigmaria remnants of a small-celled tissue on the outside of 

 what has generally been taken to be the superficial layer of the Stigmarian axis, 

 and a careful investigation of this point inclines me to agree with him that very 

 probably the Stigmarian rootlets were actually formed like those of Isoetes, some- 

 what below the surface layer, which, after the emergence of the- rootlets, became 

 partially disorganised. Should this surmise prove correct, when apices of 

 Stigmaria showing structure come to light, the last real difference between the 

 rootlets of Isoetes and the rootlets of Stigmaria will have disappeared, and the 

 view for which Professor Williamson so strongly contended will be finally 

 established. 



While a careful comparison of Isoetes with the extinct Lycopodiaceous plants 

 may be taken finally to settle its systematic position, the Psilotaceae have been 

 somewhat disturbed by such comparisons. Placed formerly without much hesita- 

 tion in the phylum Lycopodiales, certain features in their organisation, such as 

 the dichotomy of their sporophylls, and the structure of their fructification 

 generally have suggested affinity with that interesting group of extinct plants, 

 the Sphenophyllales. Their actual inclusion in this group by Thomas and by 

 Bcwer may seem, perhaps, somewhat hazardous, considering the differences 

 existing between the Psilotaceae and Sphenophyllum ; and the more cautious 

 attitude of Seward, in setting up a separate group for these forms, seems on the 

 whole more satisfactory than forcing these aberrant relatives of the Lycopods into 

 the somewhat Procrustean bed of Sphenophyllales, which necessitates the 

 minimising of such important differences as the dichotomous branching of the 

 axis and the alternate arrangement of their leaves, though the latter character 

 allows, it is true, of some bridging over. But, even adopting this more cautious 

 attitude, the study of the Sphenophyllales has been of great help in coming 

 to a clearer understanding of certan morphological peculiarities of the Psilo- 

 taceae, quite apart from the flood of light which this synthetic group of Spheno- 

 phyllales has thrown upon the relationship of the Lycopodiales to the Equi- 

 setales. 



More far-reaching in its bearing on the relationships of existing plants has 

 been the study of those interesting fern-like plants, which seem to show in their 

 vegetative organs a structure possessing both fern-like and Cycadean affinities. 

 Full of interest as these so-called Cycadofilices were in their vegetative organisa- 

 tion', they were destined to rivet on themselves the attention of all botanists by 

 the discovery of their fructifications. No chapter in the recent history of 

 Paleobotany is more thrilling than the discovery, by the patient and thorough 

 researches of Professor Oliver, of the connection between Lyginodendron and 

 the well-known palaeozoic seed, Lagenostoma. With Dr. Scott as sponsor, this 

 new and startling revelation met with ready acceptance, and, thanks to the 

 indefatigable energies of Palaeobotanists, no fossil fern seemed at one time safe 

 from possible inclusion among the Pteridospermae. 



The infectious enthusiasm with which the discovery of the seed-bearing habit 

 of the Lyginodendreae and the Medullosae was greeted carried all before it, and 

 we in England particularly have perhaps not looked carefully enough into the 

 foundations upon which rested the theory that these groups form the ' miss- 

 ing links ' between the Ferns and Cycads. A criticism against the wholesale 

 acceptance of this view has been put forward by Professor Chodat, 2 of Geneva, 

 that distinguished and versatile botanist whom we have on several occasions 

 had the pleasure of welcoming in our midst. Couched throughout in friendly 

 and courteous language, and full of admiration for the work of those who were 

 concerned in the establishment of the group of Cycadofilices, now termed 



2 Chodat, K. : 'Les Pteropsides des temps paleozoi'ques,' Archives des 

 Sciences physiques et naturelles, Geneve, tome xxvi., 1908. 



