120 



point 



in 



THE CAUSES OF FLUCTUATIONS IN TUEGESCENCE 



ipect to relations between supply and loss of water 



The abnormal drain 



on 



incision. 



the general stock of liquid within the tissues is purely temporary in cases of 



longer the case where portions of tissue are killed by applica- 

 dinary application of heat to a particular point implies the death 



But this 



of heat 



Any 



of considerable masses of tissue and 



we have already seen 



> 



any 



dead 



mass of 



presents a permanent site of abnormally excessive drain upon the general stock 



of liquid. The details which were given in Chapt 



II 



garding the phenomena 



occurring in connection with the death of portions of axes or rachises under the influence 



of the vapour of chloroform and heat are 

 fact is of course constantly brought befor 



sufficient to show that this is the 



and the 



keep 



g 



portions of a leaf 



3 us by the difficulty which is encountered in 

 shoot turgid beyond any point in which the tissues have 

 been killed by means which do not in any way interfere with the efficiency of the 

 water-conducting system, whenever external conditions are such as to favour active 

 evaporative loss. In cases of the application of heat, then, we do not merely determine 

 temporary exudative and evaporative loss in the site of application and its immediate 

 neighbourhood; but we also almost inevitably establish a permanent abnormal drain 

 upon the water-supply generally, and with this the liability to diffusion of move- 

 ments naturally increases. 



In cases of contact-" stimulat 



we induce mere local redistributions of liquid 



within the tissues; in 



of 



we give rise to temporary 



dative loss fr 



the general supply of liquid; in cases of heating we secure not only this, but in 



add 



we establish temporary 



transpiratory loss and a site of persistent 

 The tendency to diffusion of movement is at a minimum in cases 

 of contact; in cases of incision it increases; in cases of heating it rises to a maxi- 



abnormal dr 



Tli 



mum. 



affords 



dependent 



two sets of facts run parallel with one another, and the former of them 



an 



planation of the latter, if 

 fluctuations in the relatic 



we 



pt the view that the movements are 



existing bet 



pply and loss of liquid 



If, on the other hand, we insist on adhering to the popular theory, we must be con- 



tent to assume that 



contact, incision, and heat 



stimuli which differ from one anothe 





in their capacity for inducing active protoplasmic contraction 



CHAPTER XII. 



cmsts of the propagation of mobements in Jfttmosa pnoica. 



Whilst the movements of the various parts of the leaves of Mimosa pudiea have 



ascribed to the action of certain special masses of irritable 



by common consent been 



and contractile tissue in the motor organs, several distinct theo 



to es 



have been advanced 



the phenomenon of the diffusion of movements beyond the site in which 



they are originally induced 



ording to the ordinarily accepted theory, to explain the 



diffusion of "stimulation" from one part to another. According to the older observers, 

 Dutrochet, Sachs, Hoffmeister and Pfeffer, fluctuations in the pressure of the current 

 of liquid traversing the wood played the part of mechanical stimuli to th 







irr 



itable 



and contractile elements in the tissue of the motor organs. At a later period, and when 



was first attracted to the fact that 



table tissues are not isolated, but 



general 



the protoplasts of vege- 



connected with one another so as to f 



a con- 





tinuous reticulum 



) 



attempt was made to substitute 



for a mechanical the or} 



