So RESEARCHES ON IRRITABILITY OF PLANTS 



large, and the difference between the pairs in the series goes 

 on increasing. The sum of heights of pairs of successive 

 responses remains however approximately the same. The 

 odd numbers in the series decline continuously (i) 18-5, 

 (3) 16, (5) 11, (7) 6 ; whereas the responses in the even 

 series grow in amplitude (2) 25*5 (4) 30, (6) 33. 



Table giving Heights of Successive Responses 



Fatigue-reversal under Tetanisation 



If the Mimosa leaf be subjected to continuous stimulation 

 it has been found that, after the preliminary fall, it re-erects 

 itself in spite of the stimuli which are still acting upon it. 

 This at first sight would appear to be very perplexing, 

 but the apparent anomaly would however disappear when we 

 recognise the essential unity of response in the plant and the 

 animal. A frog's muscle, under continued tetanising electric 

 shocks, at first exhibits the normal contraction, but after- 

 wards relaxes, in' spite of the excitation to which it is being 

 subjected (fig. 41). The difference between the normal 

 relaxation of recovery (expansion) and this fatigue-relaxa- 

 tion induced under continuous stimulation, lies in the fact 

 that in the former case response takes place on renewed 

 stimulation, while in the latter the tissue has become 



