88 Chapters in Modern Botany CHAP. 



of the protoplasm " which has been discovered in the tissue 

 of this cushion at least so far as propagation of impulse 

 is concerned, for contractility of the network cannot be 

 assumed. The most recent theory on the matter is that of 

 Professor Haberlandt, who by means of very careful 

 anatomical researches has been led to conclude that the 

 stimulus travels down a continuous set of tubular conduct- 

 ing cells included in the bast portion of the leaf-strands. 

 He believes that the transmission depends upon changes 

 of hydrostatic pressure induced in the tubular cells and on 

 resulting movements of the cell-sap ; in other words, that 

 it is not due to any particular nervous excitability of the 

 living matter. But anatomical researches alone cannot 

 justify such a conclusion ; nor is it easy to see how to prove 

 or disprove it by direct experiment. 



The movements of the tentacles of the Sun-dew, of the 

 leaves of Dionasa, of the irritable stamens of the Rockrose 

 (Helianthemum), Barberry, etc., the closure of the stigma 

 lips of a Mimulus upon a pollen-grain, the bending of a 

 tendril when touched, are also to be distinguished from that 

 series of movements to the discussion of which this chapter 

 has been devoted ; and no doubt reserve a wide and varied 

 field for a future generation of subtle experimentalists. For 

 instead of the animal world alone possessing movement, 

 and the plant standing passive, the phenomena of plant 

 movement, while of course less obvious in amount, seem to 

 be not only the more varied in kind, but perhaps also in 

 cause. 



Summary. The different kinds of movement may be 

 arranged as follows : 



A. Movements of Growing Parts 



(i) " Spontaneous " movements that is to say those 

 whose conditions are not known, e.g. the revolving 



