458 LIFE MOVEMENTS IN PLANTS 



the same as 1"^! =1-4. Hence we arrive at the following 



law : 



The i)itensity on geotropic action varies as the sine of the 



directive angle. 



METHOD OF VERTICAL ROTATION. 



I have hitherto described results obtained with the 

 Method of Axial Rotation ; I shall now take up the 

 second method, that of Vertical Rotation, diagrammatic 

 representation of which is given in figure 166V. The speci- 

 men is held vertical and two electrical contacts, A and 

 B, made with the two lateral sides ; it is then rotated 

 round a horizontal axis perpendicular to the length of the 

 specimen. ' Rotation may be carried in a right-handed 

 direction with increasing angle with the vertical. The 

 point A is thus subjected to enhanced geotropic stimula- 

 tion and exhibits increasing electric change of galvano- 

 metric negativity ; continuous decrease of angle of inclina- 

 tion to zero by rotation in the reverse direction causes a 

 disappearance of the induced electric change. The rota- 

 tion is next continued in the negative direction by which 

 the point B is increasingly subjected to geotropic action. 

 H is now found to exhibit excitatory reaction, the current 

 of response having undergone a reversal. Rotation to the 

 right and left will be distinguished by plus and minus 

 signs. 



ELECTRIC RESPONSE THROUGH AN ENTIRE CYCLE. 



Experiment 177. — When the specimen is vigorous, charac- 

 teristic response with its changing sign may be obtained 

 through an entire cycle from 0° to -f- 4o^ to -H 9() ' ; then 

 back to 45=" to 0^ to -45° to -90°. With less vigorous speci- 

 mens the responses becomes enfeebled under fatigue. I give 



