90 RESEARCHES ON IRRITABILITY OF PLANTS 



ozone, was showing signs of fatigue, as evidenced by the 

 gradual diminution of the heights of successive responses. 



Fig. 46. — Stimulating action of ozone. 



Fig. 47. — Effect of carbonic-acid gas. 



The introduction of ozone brought, however, an immediate 

 change ; the induced enhancement of excitabihty is seen 



