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SCIENCE 



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



out, a very old one, and in adopting it we 

 re-connect with the period of develop- 

 mental morphology. Since the limited 

 time at my disposal forbids adequate ref- 

 erence to historical details, and to the work 

 and thought of many botanists in this field, 

 let me in a word disclaim any originality in 

 trying to express in relation to some mor- 

 phological problems what seems to me the 

 significant trend, in part deliberate and in 

 part unconscious, of morphology at present. 

 The methods available in causal mor- 

 phology are the detailed study in selected 

 plants of the normal development and its 

 results, comparison over as wide an area 

 as possible, with special attention to the 

 essential correspondences (homologies of 

 organization) arrived at independently, 

 the study of variations, mutations, and ab- 

 normalities in the light of their develop- 

 ment, and ultimately critical experimental 

 work. This will be evident in the follow- 

 ing attempt to look at some old questions 

 from the causal point of view. I shall take 

 them as suggested by the fern, without 

 confining my remarks to this. The fern 

 presents all the main problems in the mor- 

 phology of the vegetative organs of the 

 higher plants, and what little I have to 

 say regarding the further step to the seed- 

 habit will come as a natural appendix to 

 its consideration. 



Twice in its normal life-history the fern 

 exhibits a process of development starting 

 from the single cell and resulting in the one 

 case in the prothallus and in the other in 

 the fern-plant. For the present we may 

 treat these two stages in the life-history as 

 individuals, their development presenting 

 the same general problems as a plant of, 

 say, Fucus or Enteromorpha, where there 

 is no alternation of generations. How is 

 the morphologist to regard this process of 

 individual development ? 



In the first place, we seem forced to re- 



gard the specific distinctness as holding for 

 the germ as well as the resulting mature 

 plant, however the relation between the 

 germ-cell and the characters of the devel- 

 oped organism is to be explained. We start 

 thus with a conception of specific substance, 

 leaving it quite an open question on what 

 the specific nature depends. This enables 

 us to state the problem of development freed 

 from all considerations of the ultimate 

 uses of the developed structure. The course 

 of development to the adult condition can 

 be looked upon as the manifestation of the 

 properties of the specific substance under 

 certain conditions. This decides our atti- 

 tude as morphologists to the functions of 

 the plant and to teleology. Function does 

 not concern us except in so far as it is 

 found to enter as a causal factor into the 

 process of development. Similarly, until 

 purpose can be shown to be effective as a 

 causal factor it is merely an unfortunate 

 expression for the result attained. 



Let me remind you, also, that the indi- 

 vidual plant, whether it be unicellular, 

 coenoeytic or multicellular, may behave as 

 a whole at all stages of its development. 

 We see this, for instance, in the germina- 

 tion of (Edogonium, in the germination and 

 subsequent strengthening of the basal 

 region in Fucus or Laminaria, in the moss- 

 plant or fern-plant, or in a dicotyledonous 

 tree. A system of relations is evident in 

 the plant, expressed in the polarity and the 

 mutual influences of the main axis and lat- 

 eral branches, as well as in the influences 

 exerted on the basal region by the distant 

 growing parts. We thus recognize, in its 

 most general form, the correlation of parts, 

 a concept of proved value in botany. 



To some the expression of the observed 

 facts in this way may appear perilously 

 mystical. I do not think so myself. It is 

 true that the nature of the specific sub- 

 stance and of the system of relations is xm- 



