1914] on Plant-Autographs and their Revelations 183 



When brought suddenly from darkness to lioht, there is also a 

 transient depression followed by enhanced excitability. 



Temperature has also a marked effect on excitability. Up to a 

 critical point warmth increases excitabihty, the recovery beino; also 

 hastened. Cooling conversely depresses excitability. The motile 

 excitabilitv is abolished at about 20° C. 



Effect of Air, Food, and Drugs. 



The plant is intensely susceptible to the impurities present in the 

 air. The vitiated air of the town has a very depressing effect. 

 According to popular science, what is death to the animal is supposed 



Fig. 8. — Effect of Carbonic Acid Gas. 



to be life for the plant; for does it not flourish in the deadly 

 atmosphere of carbonic acid gas ? The record (Fig. 8) shows that, 

 instead of flourishing, the plant gets suffocated just like a human 

 being. Note the gasp of relief when fresh air is introduced. Only 

 in the presence of sunlight is the effect modified by photosynthesis. 

 In contrast to the effect of carbonic acid, ozone renders the plant 

 highly excitable. Sulphuretted hydrogen, even in small quantities, 

 is fatal to the plant. Chloroform acts as a strong narcotic, inducing 

 a rapid abolition of excitability. The kidicrously unsteady gait of 



