420 



NA TURE 



[September 3, 1908 



occur at the same time-intervals as the stimuli is obviously 

 the striking feature of the case. If the pendulum-like 

 swing always tended to occur naturally in a twelve hours' 

 rhvthm it would be a different matter. But Pfeffer has 

 shown that a rhythm of six hours can equally well be 

 built up. And the experiments of Miss Pertz and myself ' 

 show that a half-hourly or quarter-hourly rhythm can be 

 produced by alternate geotropic stimulation. 



We are indebted to Keeble " for an interesting case of 

 apparent habit among the lower animals. Convoluia 

 roscoffensis, a minute worm-like creature found on the 

 coast of Brittany, leads a life dependent on the ebb and 

 flow of the sea. When the tide is out the Convoluta come 

 to the surface, showing themselves in large green patches. 

 As the rising tide begins to cover them they sink down 

 into safer quarters. The remarkable fact is that when 

 kept in an aquarium, and therefore removed from tidal 

 action, they continue for a short time to perform rhythmic 

 movements in time with the tide. 



Let us take a human habit, for instance that of a man 

 who goes a walk every day and turns back at a given 

 mile-post. This becomes habitual, so that he reverses his 

 walk automatically when the limit is reached. It is no 

 explanation of the fact that the stimulus which makes 

 him start from home includes his return — that he has a 

 mental return-ticket. .Such explanation does not account 

 for the point at which he turns, which as a matter of 

 fact is the result of association. In the same way a man 

 who goes to sleep will ultimately wake; but the fact that 

 he wakes at four in the morning depends on a habit built 

 up by his being compelled to rise daily at that time. Even 

 those who will deny that anything like association can 

 occur in plants cannot deny that in the continuance of the 

 nyctitropic rhythm in constant conditions we have, in 

 plants, something which has general character of habit, 

 i.e., a rhythmic action depending on a rhythmic stimulus 

 that has ceased to exist. 



On the other hand, many will object that even the 

 simplest form of association implies a nervous system. 

 With regard to this objection it must be remembered that 

 plants have two at least of the qualities characteristic of 

 animals — namely, extreme sensitiveness to certain agencies 

 and the power of transmitting stimuli from one part to 

 another of the plant body. It is true that there is no 

 central nervous system, nothing but a complex system of 

 nuclei ; but these have some of the qualities of nerve cells, 

 while intercommunicating protoplasmic threads may play 

 the part of nerves. Spencer ' bases the power of associa- 

 tion on the fact that every discharge conveyed by a nerve 

 " leaves it in a state for conveying a subsequent like dis- 

 charge with less resistance." Is it not possible that the 

 same thing may be as true of plants as it apparently is of 

 infusoria? We have seen reasons to suppose that the 

 " internal conditions " or " physiological states " in plants 

 are of the nature of engrams, or residual effects of external 

 stimuli, and such engrams may become associated in the 

 same way. 



There is likely to be another objection to my assump- 

 tion that a simple form of associated action occurs in 

 plants — namely, that association implies consciousness. It 

 is impossible io know whether or not plants are conscious ; 

 but it is consistent with the doctrine of continuity that in 

 all living things there is something psychic, and if we 

 accept this point of view we must believe that in plants 

 there exists a faint copy of what we know as conscious- 

 ness in ourselves."^ 



I am told by psychologists that I must define my point 

 of view. I am accused of occupying that unscientific posi- 

 tion known as "sitting on the fence." It is said that, 

 like other biologists, I try to pick out what suits my 

 purpose from two opposite schools of thought — the psycho- 

 logical and the physiological. 



What I claim is that, as regards reaction to environ- 

 ment, a plant and a man must be placed in the same great 

 class, in spite of the obvious fact that as regards com- 

 plexity of behaviour the difference between them is 



1 Atmals of Botany, 1892 and 190^. 



2 Gamble and Keeble, O.J. Mic. Science, xlvii. p. 401. 



3 "Psychology," 2nd edit., vol. i. p. 615. 



* See James Ward, " Naturalism and Agnosticism," vol. !., Lecture X. 



enormous. I am not a psychologist, and I am not bound 

 to give an opinion as to how far the occurrence of definite 

 actions in response to stimulus is a physiological and how 

 far a psychological problem. I am told that I have no 

 right to assume the neural series of changes to be the 

 cause of the psychological series, though I am allowed to 

 say that neural changes are the universal concomitants of 

 psychological change. This seems to me, in my ignor- 

 ance, an unsatisfactory position. I find myself obliged to 

 believe that the mncmic quality in all living things (which 

 is proved to exist by direct experiment) must depend on 

 the physical changes in protoplasm, and that it is there- 

 fore permissible to use these changes as a notation in 

 which the phenomena of habit may be expressed. 



Ilcibit illustrated by Morphology. 



We have hitherto been considering the mnemic quality 

 of movements ; but, as I have attempted to show, morpho- 

 logical changes are reactions to stimulation of the same 

 kind as these temporary changes. It is indeed from the 

 morphological reactions of living things that the most 

 striking cases of habit are, in my opinion, to be found. 



The development of the individual from the germ-cell 

 takes place by a series of stages of cell-division and 

 growth, each stage apparently serving as a stimulus to 

 the next, each unit following its predecessor like the move- 

 ments linked together in an habitual action performed by 

 an animal. 



My view is that the rhythm of ontogeny is actually and 

 literally a habit. It undoubtedly has the feature which 

 I have described as preeminently characteristic of habit, 

 viz., an automatic quality which is seen in the performance 

 of a series of actions in the absence of the complete series 

 of stimuli to which they (the stages of ontogeny) were 

 originally due. This is the chief point on which I wish 

 to insist — I mean that the resemblance between ontogeny 

 and habit is not merely superficial, but deeply seated. It 

 was with this conclusion in view that I dwelt, at the risk 

 of being tedious, on the fact that memory has its place 

 in the morphological as well as in the temporary reactions 

 of living things. It cannot be denied that the ontogenetic 

 rhythm has the two qualities observable in habit — namely, 

 a certain degree of fixity or automaticity, and also a certain 

 variability. A habit is not irrevocably fixed, but may be 

 altered in various ways. Parts of it may be forgotten or 

 new links may be added to it. In ontogeny the fixity is 

 especially observable in the earlier, the variability in the 

 later, stages. Mr. Darwin has pointed out that " on the 

 view that species are only strongly marked and fixed 

 varieties, we might expect often to find them still con- 

 tinuing to vary in those parts of their structure which 

 have varied within a moderately recent period." These 

 remarks are in explanation of the " notorious " fact that 

 specific are more variable than generic character — a fact 

 for which it is "almost superfluous to adduce evidence."' 

 This, again, is what we find in habit : take the case of a 

 man who, from his youth up, has daily repeated a certain 

 form of words. If in middle life an addition is made to 

 the formula, he will find the recently acquired part more 

 liable to vary than the rest. 



Again, there is the wonderful fact that, as the ovum 

 develops into the perfect organism, it passes through a 

 series of changes which are believed to represent the 

 successive forms through which its ancestors passed in the 

 process o.f evolution. This is precisely paralleled by our 

 own experience of memory, for it often happens that we 

 cannot reproduce the last learned verse of a poem without 

 repeating the earlier part ; each verse is suggested by the 

 previous one and acts as a stimulus for the next. The 

 blurred and imperfect character of the ontogenetic version 

 of the phylogenctic series may at least remind us of the 

 tendency to abbreviate by omission what we have learned 

 by heart. 



In all bi-sexual organisms the ontogenetic rhythm of 

 the offspring is a combination of the rhythms of its 

 parents. This may or may not be visible in the offspring ; 

 thus in the crossing of two varieties the mongrel assumes 

 the character of the prepotent parent. Or the offspring 



* '* Orig:n of Specie:, 6thedi'.,p, 22. 



NO. 2027, VOL. 78] 



