tOi TRANSACTIONS OF SECTION K. 



neither formulates them as they appear to the morphologist. Together with 

 genetics, they indicate the need of recognising what I prefer to call General or 

 Causal Morphology. 



The problems of causal morphology are not new, though most of them 

 are still unsolved and are difficult to formulate, let alone to answer. As we have 

 seen, they were recognised in the time of developmental 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 problems force themselves upon 

 the ordinary morphologist, and it is from his position that I venture to approach 

 them. I willingly recognise, however, that causal morphology may also be 

 regarde-d as a department of plant-physiology. In development, which is the 

 essential of the problem, the distinction between morphology and physiology 

 really disappears, even if this distinction can be usefully maintained in the 

 study of the fully developed organism. We are brought up against a fact 

 "which is readily overlooked in these days of specialisation, that Botany is the 

 scientific study of plants. 



General morphology agrees with physiology 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, how- 

 ever, we need not be limited to a physico-chemical explanation of the plant. 

 Modern physiology rightly aims at this so far as possible, but, while successful 

 in some departments, 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 development and 

 morphological construction. The morphologist must therefore take the com- 

 plicated form and its genesis in development and strive for a morphological 

 analysis of the developing plant. This is to attack the problem from the other 

 side and to work back from the phenomena of organisation toward concepts 

 of the nature of the underlying substance. 



It is to these questions of general morphology with a causal aim (for causal 

 morphology, though convenient, is really too ambitious a name for anything we 

 yet possess) that J 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 out, a very old one, and in adopting it we re-connect ° with the period of 

 developmental morphology. Since the limited time at my disposal forbids 

 adequate reference 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 morphological problems what seems to me the signifi- 

 cant trend, in part deliberate and in part unconscious, of morphology at present. 

 The methods available in causal morphology are the detailed study in selected 

 plants of the normal development and its resuJts, comparison over as wide 

 an area as possible with special attention to the essential correspondences 

 (homologies of organisation) arrived at independently, the study of variations, 

 mutations, and abnormalities in the light of their development, and ultimately 

 critical experimental work. This will be evident in the following 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 morphology 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. 



Individual Developvient. 

 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 



' It is no mere coincidence that modern genetics is due to the re-discovery 

 of the work of an investigator of this period. 



' It will be sufficient to mention the names of Knight. Naegeli, Leitgeb. 

 Hofmeister, Vochting, Sachs, Klebs, and Goebel as the earlier workers on %hh 

 line. 



