554 



COMPARATIVE ELECTRO-PHYSIOLOGY 



the rest, and this intimate connection between outlying areas 

 becomes comprehensible, when we are made aware of the 

 easy communication afforded by the existence of specialised 

 conducting elements. 



I shall now proceed to deal with the importance ol 

 stimulus, and its conduction to the interior of the plant, as 



the essential factor in sub- 

 serving the various life- 

 activities of the organism. 

 That the reception of stimu- 

 lus is important, in main- 

 taining the excitability of a 

 plant, is easily seen in the 

 case of Mimosa, when de- 

 prived of light, for example. 

 Under these conditions, its 

 motile excitability is found 

 to disappear. And this is 

 only restored on re-exposure 

 to light. We have seen 

 again, in the course of the 

 last chapter, that the isolated 

 vegetable nerve, deprived, as 

 it is, of normal favourable 

 conditions, becomes sub-tonic 

 or moribund, and then its 

 ordinary responsive power is 

 abolished or even reversed. 

 Under these circumstances 

 the normal excitability is 

 found to be restored by the continued action of stimulus. 

 Abnormal positive response is thus found to be converted 

 into normal negative. Again, after an intervening period of 

 stimulation, response of ordinary amplitude is found, as 

 in fig- 333> to become enhanced. It is thus seen that a tissue, 

 when cut off from the supply of stimulus, loses its normal 

 excitability, and that a more or less continuous supply of 



F IG. 333- Photographic Record of 

 Effect of Tetanisation in En- 

 hancing Mechanical Response of 

 Plant-nerve 



The first series of responses heightened 

 to second series, after intermediate 

 tetanisation. 



