Decembee 3, 1915] 



SCIENCE 



783 



and with this any attempt to base ho- 

 mology on homogeny. Many of the hom- 

 ologies that exist between series of parallel 

 development are what have been happily 

 termed homologies of organization; these 

 are sometimes so close as to result in prac- 

 tical identity, at other times so distinct as 

 to be evident homoplasies. The critical 

 study of homologies of organization over 

 as wide an area as possible becomes of 

 primary interest and importance. 



Since about the beginning of the pres- 

 ent century a change of attitude towards 

 morphological problems has become more 

 and more evident in several ways. It 

 seems to be a phyletic drift affecting simul- 

 taneously a plurality of lines of thought. 

 The increasing tendency to look upon 

 problems of development and construction 

 from a causal point of view is seen in the 

 prominence given to what may be termed 

 developmental physiology, and also in 

 what Goebel has called organography. 

 These deal with the same problems from 

 different sides and neither formulates 

 them as they appear to the morphologist. 

 Together with genetics, they indicate the 

 need of recognizing what I prefer to call 

 general or causal morphology. 



The problems of causal morphology are 

 not new, though most of them are still un- 

 solved and are difficult to formulate, let 

 alone to answer. As we have seen, they 

 were recognized in the time of develop- 

 mental morphology, though they have 

 since been almost wholly neglected by 

 morphologists. So far as they have been 

 studied during the phyletic period, it has 

 been from the physiological rather than 

 the morphological side. Still, such prob- 

 lems force themselves upon the ordinary 

 morphologist, and it is from his position 

 that I venture to approach them. I will- 

 ingly recognize, however, that causal mor- 

 phology may also be regarded as a depart- 



ment of plant-physiology. In develop- 

 ment, which is the essential of the prob- 

 lem, the distinction between morphology 

 and" physiology really disappears, even if 

 this distinction can be usefully maintained 

 in the study of the fully developed organ- 

 ism. We are brought up against a fact 

 which is readily overlooked in these days 

 of specialization, that botany is the scien- 

 tific study of plants. 



General morphology agrees with physi- 

 ology in its aim, being a causal explana- 

 tion of the plant and not historical. Its 

 problems would remain if the phyletic 

 history were before us in full. In the 

 present state of our ignorance, however, 

 we need not be limited to a physico-chem- 

 ical explanation of the plant. Modern 

 physiology rightly aims at this so far as 

 possible, but, while successful in some de- 

 partments, has to adopt other methods of 

 explanation and analysis in dealing with 

 irritability. It is even more obvious that 

 no physico-chemical explanation extends 

 far enough to reach the problems of de- 

 velopment and morphological construc- 

 tion. The morphologist must therefore 

 take the complicated form and its genesis 

 in development and strive for a morpho- 

 logical analysis of the developing plant. 

 This is to attack the problem from the 

 other side, and to work back from the 

 phenomena of organization toward con- 

 cepts of the nature of the underlying sub- 

 stance. 



It is to these questions of general mor- 

 phology with a causal aim (for causal mor- 

 phology, though convenient, is really too 

 ambitious a name for anything we yet pos- 

 sess) that I wish to ask your attention. 

 All we can do at first is to take up a new 

 attitude towards our problems, and to 

 gather here and there hints upon which 

 new lines of attack may be based. This 

 new attitude is, however, as I have pointed 



