68 Chapters in Modern Botany CHAP. 



naturally, therefore, did Darwin regard the powers of 

 climbers as inherent in all the higher plants. In crowded 

 surroundings, where it is of advantage to rise, some plants 

 have retained and developed the powers of moving and 

 feeling which are latent in all. 



In the third place, while the powers of climbers are 

 often markedly influenced by temperature, by light, by 

 gravity, and other factors in their environment, it is certain 

 that these do not explain the movement, except, of course, 

 in so far as the health of the plant depends ultimately upon 

 the sufficiency of its surroundings. In short, the move- 

 ments are manifestations of the internal life of the plant. 



But by what means within the plant are they produced ? 

 Of this in his volume on Climbing Plants Darwin says 

 little, nor can we even now say anything very complete. 

 This is not greatly to be wondered at, for as we have little 

 minute knowledge as to the processes of contraction in 

 animals where we know that these are located in definite 

 structures the muscles it is not surprising that we know 

 still less as to the movements of plants which have no 

 specialised contractile elements that we can recognise. 



Sachs, Dr. de Vries, and others have suggested that the 

 rotating movement say of a twining shoot is due to un- 

 equal growth now on one side and now on another, and 

 that this again depends on altered water-tension or tur- 

 gescence in the growing cells. This suggestion was 

 accepted by Darwin, although he did not believe that it 

 could apply to those cases where rapid movement follows a 

 slight touch. This is obviously a difficulty. Furthermore, 

 the suggestion that unequal growth on different sides of the 

 stem explains the revolving movements has to face the fact 

 that the rotating movement may continue without there 

 being any observable growth. 



Without denying that the altered water-tension a.nd un- 



