254 RESEARCHES ON IRRITABILITY OF PLANTS 



protoplasm are more or less opposed, or that there is no 

 law of polar action which is of universal application. 



But we have seen that the unfibrillated protoplasm of 

 the plant exhibits polar effects which are identical with 

 those of animal tissues. It is not impossible that normal 

 polar effects may be subject to modification from the 

 influence of diverse factors, such for example as strength of 

 current, physiological condition of specimen, its age, and 

 the season of the year. When an exhaustive survey has 

 been made, it may be found that the responses of the 

 Protozoa were not, after all, anomalous, but have a place of 

 their own in some transitional type of reaction given by 

 specimens whose characteristics are definitely recognised as 

 normal. With the object of completing such a survey, we 

 may continue our detailed study of the polar reactions of 

 sensitive plants under widely different conditions. And 

 first we shall study the effects of a still further progressive 

 increase of current, in order to see whether any new pheno- 

 menon comes into the field of observation, taking the 

 reactions of the pulvinus of Mimosa first in the series. 



Primary Leaf of Mimosa 



I have employed both the bi-polar and mono-polar 

 methods. The mode of procedure was to increase the current 

 step by step from minimum to maximum, and note the 

 changing types of reaction at different critical points. With 

 vigorous specimens this can be done without any danger 

 of the onset of fatigue. After the value of certain critical 

 points has been determined, experiments were repeated with 

 fresh specimens, at and about these particular critical 

 points. I shall first describe a typical experiment with a 

 very sensitive and vigorous specimen, and for the sake 

 of simplicity I give in detail the effects observed at one 

 pulvinus only, leaving it to be understood that similar 

 effects were also induced at the other. 



The specimen, as said before, was very sensitive, and 



