ABNORMAL AND NORMAL RESPONSE 8l 



under stimulation, the rate of growth of that particular 

 specimen of Kysoor was feeble, being as low as 0-3 (j, 

 per second. As the activity of growth is an indication 

 of a healthy tone, the enfeebled rate of growth was a sign 

 of the subtonic condition of the plant. It thus appeared 

 that, other things being the same, the abnormal positive 

 is the characteristic response of the subtonic plant. 



In the parallel phenomenon of response of a pulvinated 

 organ such as the leaf of Mimosa, I have shown (i) that 

 when the tonic level of the pulvinus is helow par, the response 

 is abnormal positive, exhibited by the erectile movemicnt of 

 the leaf ; and (2) that as a result of continuous stimulation 

 the tonicity is raised to a condition of par. The 'response 

 is now changed into normal negative as indicated by the 

 fall of the leaf.^ In the responsive variation of growth, 

 likewise, the abnormal positive response of the subtonic 

 specimen was transformed into the normal negative in 

 consequence of improvement of tonic condition attained 

 under continued photic stimulation. The above facts lead 

 to the following generalisation : 



1. That while strong light induces retardation of growth 



in an organ whose tonic condition is normal or 

 above par, it induces acceleration in an organ whose 

 condition is helow par ; 



2. That by the action of the stimulus of light itself, 



a subtonic organ is raised to a condition of par, 

 with concomitant transformation of its response to 

 that of normal retardation. 



Continuity between Abnormal and Normal 



Response 



The tonic condition of a growing organ may vary widely ; 

 of this the following are the two extreme cases : (i) the 

 optimum, and (2) the subtonic. In the optimum condition 



^ The Motor Mechanism of Plants (1928), p. 51. 



