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SCIENCE 



[N. S. Vol. XLII. No. 1092 



adoption of a causal explanation as the aim 

 of morphological work. I have confined 

 myself to problems bearing on the develop- 

 ment and self-construction of the individ- 

 ual, and tried to treat them so as to illus- 

 trate the causal attitude and possible lines 

 of attack. Preliminary speculations on the 

 questions considered can at best contain a 

 germ of truth, and must be subsequently 

 adjusted in the light of further facts. I 

 have discussed these questions rather than 

 the smaller modifications in individual 

 development shown in metamorphosis, 

 partly because the latter have of late years 

 been treated from a causal point of view, 

 and partly because I wished to consider 

 questions that immediately affect us as 

 working morphologists. 



Did time allow, we should naturally be 

 led to recognize the same change of atti- 

 tude in biological science toward the prob- 

 lems of the origin of new forms. Questions 

 of bud-variation and mutation are clearly 

 akin to some of those considered, and the 

 whole subject of genetics is a special at- 

 tempt at a causal explanation of form and 

 structure and the resulting functions. 

 Close cooperation between the morpholog- 

 ical analysis of the plant and the genetic 

 analysis attained by the study of hybridi- 

 zation is most desirable. It is especially 

 desirable that both should deal with struc- 

 ture as well as with form, and in the light 

 of individual development. 



The causal factors which have determined 

 and guided evolution can be naturally re- 

 garded as an extension of the same line of 

 inquiry. The Darwinian theory, and espe- 

 cially the exposition of the principle of nat- 

 ural selection, was the greatest contribution 

 ever made to the causal explanation of the 

 organic world. Strangely enough, it led to 

 a period of morphological work in which 

 the causal aim was almost lost sight of. 

 Why evolution has taken place in certain 



directions and not in others is a problem to 

 the solution of which causal morphology 

 win contribute. The probability of ortho- 

 genesis, both in the animal and vegetable 

 kingdoms, is again coming into prominence, 

 however it is to be explained. When we 

 consider the renewed activity in this field 

 it is well to remember that, just as is the 

 case with causal morphological work, we 

 are picking up a broken thread in the botan- 

 ical web. Lastly, as if summing up all our 

 difficulties in one, we have the problem of 

 adaptation. In attacking it we must real- 

 ize that use and purpose have often been 

 assumed rather than proved. We may look 

 to scientific ecological work to help us to 

 estimate the usefulness or the selection value 

 of various characters of the plant. On the 

 other hand, causal morphology may throw 

 light on whether the "adaptation" has not, 

 in some cases at least, arisen before there 

 was a "use" for it. The hopeful sign in 

 the recent study of these greater morpho- 

 logical problems is that the difficulties are 

 being more intensely realized, and that 

 rapid solutions are justly suspect. The 

 more the causal attitude is adopted in ordi- 

 nary morphological work, the more hope 

 there is of these larger questions being 

 inductively studied rather than argued 

 about. 



The causal aim is essentially different 

 from the historical one, but there is no op- 

 position between causal and phyletic mor- 

 phology. They are rather mutually help- 

 ful, for there has been an evolution, not of 

 mature plants, but of specific substances 

 exhibiting development. A deeper insight 

 into the nature of ontogeny is thus bound 

 to be of assistance to phyletic morphology, 

 while the tested results of phyletic work 

 afford most valuable guidance in general 

 causal morphology, though this can not ac- 

 cept any limitation to single lines of descent 

 in its comparisons. 



