32 RESEARCHES ON IRRITABILITY OF PLANTS 



contractile effect in the more sluggish smooth muscles. 

 Vegetal protoplasm also is commonly regarded as little 

 capable of excitation by these shocks, behaving in this 

 respect like the sluggish smooth muscles amongst animal 

 tissues. Again, while the break-induction-shock of higher 

 intensity and shorter duration is more effective in exciting 

 the quickly reacting skeletal muscle, in the case of the 

 sluggish smooth muscle it is the make-shock of low inten- 

 sity and long duration that proves more efficacious. That 



^M^iliiii 



Fig. ii. — Arrangement for applying single make- or break-shock; 

 k, key in the primary circuit. The secondary circuit may be 

 short-circuited by the second key. 



the inference commonly made about the reaction of vegetal 

 protoplasm to single induction-shocks is not of universal 

 application, is strikingly seen in the response of pulvinus 

 of Mimosa. Here, so far at least as single induction- 

 shocks are concerned, its reaction appears more analogous 

 to that of skeletal than of smooth muscle ; as a position 

 of the secondary in relation to the primary can be found 

 in which, while a single make-shock is ineffective, a single 

 break-shock is quite efficient. In order to render the make- 

 shock effective, the secondary has here to be pushed in 

 nearer to the primary, thus increasing the intensity of the 

 shock. A pair of records will be given in a later chapter 



