IRRITABILITY OF PLANTS 149 



next result is in the nature of an anticlimax, where the 

 plant has drunk pure water not wisely, but too well. The 

 gorged plant loses all power of movement. The plant was 

 restored to normal condition by extracting the excess of liquid 

 by application of glycerine. 



Does the plant feel the depressing effect of darkness ? Fig. 15 

 records the effect of a passing cloud ; the slight variation of 

 light was detected by the plant much earlier than by the 

 observer. Any sudden change of light is found to [exert a 

 marked depressing effect. The plant partially regains its 



FIG. 14. Depression of excitability under carbonic 

 acid and revival on readmission of fresh air. 



sensibility when accustomed to darkness. When brought 

 suddenly from darkness to ligrit, there is also a transient 

 depression followed by enhanced excitability. 



Again as to the effect of wounds : 



I undertook three investigations, on the effect of wounds on 

 plants. The first enquiry is as to the effect of injury on growth ; 

 the second is the change manifested in the pulse-beat of rhythmic 

 tissues in plants. The third investigation had for its object 

 the study of the paralysing effect of wounds. 



In the first of these the normal rate of growth and change of 

 that rate by injury were found from the automatic records given 

 by the Crescograph. When the growing plant was pricked with 



