December 3, 1915] 



SCIENCE 



781 



fluence of the theory of descent. I fully 

 recognize the interest of the phyletic ideal, 

 but am unable to regard it as the exclusive, 

 or perhaps as the most important, object 

 of morphological investigation. To accept 

 the limitation of morphology to genealog- 

 ical problems is inconsistent with the pro- 

 gress of this branch of study before the 

 acceptance of the theory of descent, and 

 leaves out many of the most important 

 problems that were raised and studied by 

 the earlier morphologists. 



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 characterized by an intimate connec- 

 tion between morphological and physio- 

 logical work. Among its contributions 

 were studies of development or "growth 

 histories" of whole plants and their mem- 

 bers. 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 Morphologic" 

 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 revolu- 

 tionary, and, as in all revolutions, some of 

 the best elements of the previous regime 

 were temporarily obscured. This exces- 

 sive influence of the theory of descent 

 upon morphology did not come from Dar- 

 win himself, but from his apostle Haeckel, 

 who gave a very precise expression to the 

 idea of a genealogical grouping of animals 

 and plants, illustrated by elaborate hjT)o- 

 thetical 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 de- 

 votion of morphology to questions of rela- 

 tionship, but in the attempts made to base 

 homologies upon descent only. Lankes- 

 ter's idea of homogeny can be traced to 

 the influence of Haeckel, and nothing 

 shows the consistency of phyletic mor- 

 phology to its clear but somewhat narrow 

 ideal so plainly as the repeated attempts 

 to introduce into practise a sharp distinc- 

 tion between homogeny and homoplasy. 



Professor Bower, in his address last year 

 and in other papers, has dealt illumina- 

 tingly with the aims and methods of phy- 

 letic morphology. I need only direct at- 

 tention to some aspects of the present posi- 

 tion of this, which bear on causal mor- 

 phology. The goal of phyletic morphology 

 has throughout been to construct the gene- 

 alogical 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 genealog- 

 ical tree, since that first very complete 

 monophyletic one by Haeckel, affords a 

 clear example of a reduction series. The 

 most recent and trustworthy graphic rep- 

 resentations 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-relation- 

 ships of the AlgEe, Bryophyta, and Pteri- 

 dophyta. Regarding the Algae 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 



