THE PHOTOTROPIC CURVB AND ITS CHARACTERISTICS 351 



its tropic movement under continuous action o£ light 

 applied on one side of tlie organ. 



Experiment 134. — I give below the characteristic curve 

 of excitation (Fig. Ili2) of the pulvinus of Erytht'ina indica, 

 traced bj- the plant itself, and exactly reproduced by photo- 

 mechanical process. A parallel beam of light from a Nernst 



Fig. 131. Fig. 132. 



Fk4. 131. — Characleristic curve of iron under increasing magnetising force. 

 (.A.fter Ewing). 



Fig. 132. — Simple characteristic cnrve of photolropic reaction. Excitation 

 increases slowly in the first part and lapidiy in the .second : it is uniform in 

 the third, and undergoes decline in the fourth part {Erythrina indica). 



lamp was thrown on the upper leaf- of the pulvinus, and 

 the increasing positive curvature was recorded on a smoked 

 glass plate which was moved at an uniform rate. The 

 successive dots are at intervals of 20 seconds ; the horizontal 

 distances between successive dots are equal, and represent 

 equal increments of stimulus ; the vertical distances between 



