TRANSMISSION OF EXCITATORY WAVES IN PLANTS 25 1 



ments in the fibro- vascular bundle which were concerned in 

 transmitting the disturbance in Mimosa. This transmission 

 was, however, regarded rather as a hydro-mechanical than 

 as a true excitatory propagation. Such a conclusion, 

 as we have already seen, appeared at one time to be 

 probable in the light of the experiment on the trans- 

 mission of excitation through a narcotised area. I have, 

 however, already shown on p. 229, that abolition of motile 

 excitability need not always imply the abolition of conduc- 

 tivity. Haberlandt describes an experiment according to 

 which the excitation in Mimosa is said to have been propa- 

 gated over dead tracts of the petiole, these portions having 

 been destroyed by scalding. But it is extremely difficult to 

 ensure the death of interior tissue by such means as super- 

 ficial scalding. I have found that a portion of a plant-tissue 

 when subjected locally to the action of boiling water, after- 

 wards exhibited signs of true excitatory electric response. 

 It is only by prolonged immersion in boiling water that one 

 can be quite sure that the interior tissue is really killed by 

 scalding, and unless this is done thoroughly it is easy to see 

 that the inner cells may conduct the stimulus. 



There is, moreover, another possibility, that of pseudo- 

 conduction, by which the effect of stimulus might appear to be 

 transmitted across dead areas. My meaning will perhaps be 

 clearer if we imagine two isolated muscle-preparations, one 

 of which is attached to a striking lever, under which is the 

 -second. Supposing stimulus to be applied to the first of 

 these, we can see that it would cause the lever to strike the 

 second muscle, thus causing excitation. In this way, the 

 effect of a stimulus applied to the first muscle would appear 

 to have been transmitted to the second, completely isolated 

 from it. In reality, however, this was not a case of true, but 

 of pseudo-conduction, the excitation of the second muscle 

 being started de novo by the blow of the lever, itself only a 

 secondary effect of the excitation of the first. 



Similarly, we may have, in Haberlandt's experiment, two 

 living tissues isolated from each other by an intervening area 



