PRESIDENTIAL ADDRESS. 551 



marvellous historical account of the rise of botanical knowledge up to the years 

 1880 or 1890, he would undoubtedly have drawn attention to the remarkable 

 growth of our knowledge of extinct plants gained by Binney and Williamson 

 from the plant remains in the calcareous nodules of English coal-seams, and by 

 Renault from the siliceous pebbles of Autun. We are not likely to forget the 

 pioneer work of these veterans, though since then investigations of similar con- 

 cretions from the coal deposits of this and other countries have been undertaken 

 by numerous workers and have revealed further secrets from that vast store o'f 

 information which lies buried at our feet. 



The possibilities of impression material had indeed been practically exhausted 

 in 1870, and further advance could only come from new methods of attacking 

 the problems that still remained to be solved. The most striking recent instance 

 of the insufficiency of the evidence of external features alone was Professor 

 Oliver's demonstration of the seed-bearing nature of certain fern-like plants, based 

 on microscopical comparison of the structure of the cupule of Lagenostoma with 

 the fronds of Lyginodendron, after which discovery confirmatory evidence speedily 

 came to hand from numerous plant impressions examined by Kidston, Zeiller, 

 and other observers. 



Undoubtedly in the hands of a less competent and far-sighted observer than 

 Williamson, the new means of investigation might have proved as misleading 

 as the old method had been in many instances. Indeed, as is well known, the 

 recognition in the sections of Calamites and Sigillarias of the presence of 

 secondary wood had caused Brongniart to place these plants among conifers, 

 owing to his belief that no Vascular Cryptogams exhibited exogenous growth in 

 thickness. It required all Williamson's eloquence and pugnacity to convert both 

 British and French palasobotanists to his views, ultimately accepted with such 

 handsome acknowledgment by Grand' Eury, one of his antagonists, in his 

 ' Geologie et Palasontologie du Bassin Houiller du Gard.' 



It is curious that Grand' Eury refers in his introduction to the discovery of 

 traces of secondary growth in Ophioglossum, and not to that of Isoetes, a plant 

 much more nearly related, as we now believe, to the Lepidodendraceae, and the 

 structure of which had been so thoroughly investigated by Hofmeister. William- 

 son, it is true, refers to the secondary growth in the stem of Isoetes in his memoir 

 on Stigmaria, but compares it with the peri derm- forming cambium of that plant, 

 and does not therefore recognise any agreement in the secondary growth of these 

 two plants. 



Adopting Von Mohl's interpretation of the root-bearing base of the Isoetee 

 plant as a ' caudex descendens,' Williamson instituted a morphological compari- 

 son between the latter and the branching Stigmaria, and came to the conclusion 

 that they were homologous structures, a view which, as we heard at Sheffield, 

 is supported by Dr. Lang on the strength of a re-examination of the anatomy of 

 the stock of Isoetes. If we do not accept Williamson's interpretation of the 

 Stigmarian axis as a downward prolongation of caulome nature, the question 

 remains open whether this underground structure represented a leafless modifica- 

 tion of a normal leaf-bearing axis such as is known in the leafless rhizoms of 

 Neottia and other saprophytic plants, or whether the Stigmarian axes were mor- 

 phological entities of peculiar character. Grand' Eury, in comparing them with 

 the rhizoms of Psilotum, accepted the former alternative and, apart from mor- 

 phological considerations, was led to this view by the fact that he had observed 

 aerial stems arising in many instances, as buds on the horizontal branches of Stig- 

 maria. Confirmation of this mode of growth is still required, but it is quite 

 conceivable that there may have been a mode of vegetative reproduction in the 

 Stigmaria? analogous with that of Ophioglossum. 1 



The alternative interpretation of the Stigmarian axes as special morphological 

 entities has received weighty support from Scott and Bower, who consider them 



1 It is of interest in this connection to note that Potonie has recently put 

 forward the suggestion that many of these vertical outgrowths from the more or 

 less horizontal Stigmarian axes, some of which, as figured and described by 

 Goldenberg, taper off rapidly to a point, without any trace of ramification, may 

 be comparable with the conical ' knees ' of Taxodium, and represent woody 

 pneumatophores so common in the Swamp Cypress and other swamp-inhabiting 

 trees. 



