702 TRANSACTIONS OF SECTION K. 



In the history of morphology, after it had ceased to be the handmaid of the 

 systematic botany of the higher plants, we may broadly distinguish an idealistic 

 period, a developmental period, and a phyletic period. The period of develop- 

 mental morphology, the most fruitful and the most purely inductive in our 

 science, was characterised by an intimate connection between morphological and 

 physiological work. Among its contributions were studies of development or 

 ' o-rowth histories ' of whole plants and their members. These were carried out, 

 in part at least, in order to investigate the nature of development, and such 

 general problems found their expression at the close of the period in the 

 ' Allgemeine Morphologie ' of Hofmeister. The ' Origin of Species ' took some 

 years before it affected the methods and aims of botanical work. Then its 

 effect on morphology was revolutionary and, as in all revolutions, some of the 

 best elements of tlie previous regime were temporarily obscured. This exces- 

 sive influence of the theory of descent upon morphology did not come from 

 Darwin himself but from his apostle Haeckel, who gave a very precise expres- 

 sion to the idea of a genealogical grouping of animals and plants, illustrated 

 by elaborate hypothetical phylogenetic trees. Such ideas rapidly dominated 

 morphological work, and we find a special ' phylogenetic method ' advocated by 

 Strasburger.' The persistence of the phyletic period to the present time is 

 shown not only in the devotion of morphology to questions of relationship but in 

 the attempts "made to base homologies upon descent only. Lankester's idea of 

 homogeny can be traced to the influence of Haeckel, and nothing shows the con- 

 sistency "of phyletic morphology to its clear but somewhat narrow ideal so plainly 

 as the repeated attempts to introduce into practice a sharp distinction between 

 homogeny and homoplasy. 



Professor Bower, in hie Address last year and in other papers, has dealt 

 illuminatingly with the aims and methods of phyletic morphology. I need only 

 direct attention to some aspects of the present position of this, which bear on 

 causal morphology. The goal of phyletic morphology has throughout been to 

 construct the genealogical tree of the Vegetable Kingdom. In some ways this 

 seems farther off than ever. Phyletic work has been its own critic, and the 

 phylogeny of the genealogical tree, since that first very complete monophyletic 

 one by Haeckel, affords a clear example of a reduction series. The most recent 

 and reliable graphic representations of the inter-relationships of plants look more 

 like a bundle of sticks than a tree. Consider for a moment our complete 

 ignorance of the inter-relationships of the Algie, Bryophyta, and Pteridophyta. 

 Eegarding the Algfe we have no direct evidence, but the comparative study of 

 existing forms has suggested parallel developments along four or more main 

 lines from different starting-points in a very simple unicellular ancestry. We 

 have no clue, direct or indirect, to the ancestral forms of the Bryophyta, and it is 

 an open question whether there may not be as many parallel series in this group 

 as in the Alg;e. The Pteridophyta seem a better case, for we have direct 

 evidence from fossil plants as well as the comparison of living forms to assist 

 us. Though palreobotany has added the Sphenophyllales to the existing groups 

 of Vascular Cryptogams and has greatly enlarged our conceptions of the others, 

 there is no proof of how the great groups are related to one another. As in the 

 Bryophyta, they may represent several completely independent parallel lines. 

 There is no evidence' as to what sort of plants the Pteridojihyta were derived 

 from, and in particular none that relates them to any group of Bryophyta or 

 Algffl. I do not want to labour the argument, but much the same can be said 

 of the seed-plants, though there is considerable evidence and fairly general 

 agreement as to some Gymnosperms having come from ancient Filicales. The 

 progress of phyletic work has thus brought into relief the limitations of the 

 possible results' and the inherent diflSculties. As pointed out by Professor 

 Bower, we can hope for detailed and definite results only in particularly favour- 

 able cases, like that of the Filicales. 



The change of attitude shown in recent phyletic work towards ' parallel 



' The claims of. this phylogenetic method were at once criticised by Braun, 

 in a form that deserves 'caieful study to-day {Mcni(it.<h. d. K. Alrul. Wi.-'X. 

 V..K-]\n. 1875, p. 243 ff.). 



