358 LIFE MOVEMENTS IN PLANTS 



maximum positive value in the course of 18 minutes ; 

 after this the curve underwent a reversal, and complete 

 neutralisation occurred after a further period of 24 minutes 

 (Fig. 133). Beyond this the induced curvature is negative. 



Fig. 133. — Complete phototropic curve given by pulvinated Eq. organ. 

 Positive curvature above, and negative curvature below the horizontal zero line. 

 Preliminary negative phase of responste due to .sub-minimal stimulus. The posi- 

 tive increases, attains a maximum, and undergoes a reversal. Successive dots 

 at intervals of 30 seconds. Abscissa represents duration of exposure and quantity 

 of incideut light. (Terminal leaflet of Desmodium /jyram.) 



Complete phototfipic curve of <j rowing organs : Experi- 

 ment 186. — I obtained very similar effects by subjecting 

 the seedling of Ze:i Mays to unilateral light from an arc 

 lamp for two hour.-i. The characteristic of this curve is 

 similar to that given by the terminal leaflet of Desmodiiim 

 gyrans. At the first stage, the sub-minimal stimulation 

 is seen to induce a negative curvature, transformed into 

 positive after an interval of 10 minutes. The maximum 

 positive curvature is reached after 50 minutes, and neutra- 

 lisation completed in a further period of 43 minutes 



