phesident's address. 13 



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 association on the fact that 

 every discharge conveyed by a nerve * leaves it in a state for conveying 

 a subsequent like discharge 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 

 etFects of external stimuli, and such engrams may become associated in 

 the same way. 



There is likely to be another objection to my assumption that a simple 

 form of associated action occurs in plants — namely, that association 

 implies consciousness. It is impossible to 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 consciousness in ourselves.^ 



I am told by psychologists that I must define my point of view. I 

 am accused of occupying that unscientific position 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 psychological 

 find the physiological. 



' Psi/chology, 2nd edit., vol. i. p. 615. 



'-' See James Ward, Naturalism and Agnosticism, vol. i., Lecture X. 



