042 



STIMULUS-TRANSMITTING SYSTEM 



their characteristic movements. The appearance of this drop of liquid 

 believed by Sachs, Pfeffer and others to be a drop of water derived 

 from the woody cylinder has been quite correctly regarded as a 

 phenomenon causally related to the transmission of stimuli. 



In order to eliminate any influence which the living protoplasts 

 (including their intercellular connections) may exert over the process 

 of transmission, Pfeffer anaesthetised the middle portions of petioles 

 by means of chloroform or ether ; he found that, under these con- 

 ditions, traumatic stimuli never failed to traverse the narcotised 



Fig. 266. 



Stimulus-transmitting cells from the petiole of Mimosa pudica in L.S. The con- 

 tracted protoplasts adhere firmly to the limiting membranes of the large pits in the 

 transverse septa. Sections treated with dilute sulphuric acid and stained with 

 picric-aniline blue. 



region, while mechanical stimuli were also transmitted in a certain 

 number of cases. It has since been shown by the author himself, that 

 traumatic stimuli continue to be propagated through parts of the petiole 

 which have been killed outright by scalding. It follows, therefore, that 

 in Mimosa pudica, transmission does not depend upon the presence of a 

 continuous protoplasmic system, but consists in a disturbance of 

 hydrostatic equilibrium within the transmitting elements. A disturb- 

 ance of this kind can obviously travel through dead or anaesthetised 

 tissues ; and there is no reason to suppose that the mechanism of trans- 

 mission in the normal condition of the tissues is radically different from 

 that which prevails in scalded or narcotised organs. 



