244 



NATURE 



[October 28, 19 15 



decides our attitude as morphologists to the functions 

 of the plant and to teleology. Function does not con- 

 cern 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 ex- 

 pression for the result attained. 



Let me remind you, also, that the individual plant, 

 whether it be unicellular, coenocytic, or multicellular, 

 may behave as a whole at all stages of its develop- 

 ment. We see this, for instance, in the germination 

 of Oidogonium, 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 lateral branches, as 

 well as in the influences exerted on the basal region 

 by the distant growing parts. We thus recognise, 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 substance and of the system of relations is 

 unknown to us, but it is regarded as a subject for 

 scientific inquiry and further explanation. To recog- 

 nise fully the complexity of the substance of the plant 

 is not, however, a step towards neo-vitalism, but is 

 perhaps our best safeguard against the dangers of 

 this. 



The wholeness of the individual, together with 

 important phenomena of regeneration, has suggested 

 the conclusion that something other than physico- 

 chemical or mechanical laws are concerned in the 

 development of the organism. To this something 

 Driesch applies the name entelechy. Without dis- 

 cussing the vitalistic philosophy of the organism, or 

 other modern phases of philosophic thought that 

 treat life as an entity, it seems worth while to point 

 out that they are based mainly on the consideration 

 of animal development. It would be interesting to 

 inquire into the dif^culties that are met with in apply- 

 ing such views to plants, where regeneration in one 

 form or another is the rule rather than the exception; 

 and often does not lead to restitution of the individual. 

 Causal morphology can recognise phenomena of 

 development and of the individual, which are at pre- 

 sent beyond physico-chemical explanation, and try to 

 attack them by any methods of investigation that 

 seem practicable, without begging the main question 

 at the outset and then proceeding deductively. To 

 assume any special inner director of development, be 

 it entelechy or -vital force, is to cut the knot that may 

 ultimately be untied. 



The previous experience of botany in the time of 

 nature-philosophy may well make us cautious of 

 solving our diflRculties by the help of any new bio- 

 logical philosophy. On the other hand, co-operation 

 between biology and philosophic thought is highly 

 desirable. In this connection I should like to refer 

 to an idea contained in Prof. Alexander's paper on 

 the basis of realism. He suggests that there is only 

 one matrix from which all qualities arise, and that 

 (without introducing any fresh stuff of existence) the 

 secondary qualities, life, and at a still higher level, 

 mind, emerge by some grouping of the elements 

 within the matrix. The development of this idea as 

 it applies to life would appear to ©O'er a real point 

 of contact .between inductive biological work and 

 philosophy. 



To return to our plant, its development, with in- 

 crease in size and progressive complexity of external 

 form and internal structure, must be considered. The 

 NO. 2400, VOL. 96^ 



power of continued development possessed by most 

 plants and wanting in most animals makes com- 

 parison between the two kingdoms difficult. That 

 ' there is no fundamental difference between the con- 

 tinued and the definitely limited types of embryogeny 

 is, however, shown by plants themselves. The bryo- 

 phyte sporogonium is a clear example of the latter, 

 while the fern sporophyte is one of many examples of 

 the former. A difference less commonly emphasised 

 is that in the sporogonium (as in the higher animals) 

 the later stages of development proceed by transforma- 

 tion of the whole of the embryo into the mature or 

 adult condition ; in the fern-plant the apical develop- 

 ment results in successive additions of regions which 

 then attain their mature structure by transformation 

 of the meristematic tissue. 



These distinctions are of some importance in con- 

 sidering the generalisation originally founded on 

 animal development and known as the biogenetic law. 

 That "the ontogeny is a concise and compressed re- 

 capitulation of the phylogeny" is essentially a 

 phyletic conception. It has been more or less criti- 

 cised and challenged by some distinguished zoologists, 

 and has always been difficult to apply to plants. If 

 we avoid being prejudiced by zoological theory and 

 results, we do not find that the characters of the 

 embryos of plants have given the key to doubtful 

 questions of phylogeny. What help do they give us. 

 for instance, in the algae or the vascular cryptogams? 

 The extension of the idea of recapitulation to the 

 successively formed regions of the seedling plant re- 

 quires critical examination ; if admitted, it is at any 

 rate something different from what the zoologist 

 usually means by this. The facts — as shown, for 

 instance, in a young fern-plant — are most interesting, 

 but can perhaps be better looked at In another way. 

 Development is accompanied by an increase in size 

 of the successively formed leaves and portions of stem, 

 and the process is often cumulative, going on more 

 and more rapidly as the means increase until the adult 

 proportions are attained. The same specific system 

 of relations may thus find different expression in the 

 developing plant as constructive materials accumulate. 

 I do not want to imply that the question is merely a 

 quantitative one; quality of material may be involved, 

 or the explanation may lie still deeper. The point is 

 that the progression Is not a necessary one due to 

 some recapitulative memory. 



There . are some other classes of facts, clearly 

 cognate to normal Individual development, that seem 

 to require the causal explanation. I may mention 

 three : — (i) Vegetatlvely produced plants (from 

 bulbils, gemmae, etc.) tend in their development to 

 pass through stages in elaboration similar to young 

 plants developing from a spore or zygote. The simi- 

 larities are more striking the smaller the portion of 

 material from which a start Is made. (2) Branches 

 may repeat the stages In ontogeny more or less com- 

 pletely also In relation to differences In the nutritive 

 conditions. (3) In the course of continued develop- 

 ment there may be a return to the simpler form and 

 structure passed through on the way to the more 

 complex. These cases of parallels to, or reversals of, 

 the normal ontogenetic sequence suggest explanation 

 on causal lines, but are difficulties in the way of 

 phyletic recapitulation ; the first two cases can be in- 

 cluded under this, while the third seems definitely 

 antagonistic. On the whole, it may be said that re- 

 capitulation cannot be accepted for plants without 

 further evidence, and that preliminary inquiry dis- 

 poses us to seek a deeper and more fruitful method 

 of explaining the facts of development. 



The development of most plant-individuals starts 

 from a single cell, and when we compare mature 



