466 PLANT RESPONSE 



of the incident stimulus latent, by which its molecular mobility 

 becomes enhanced, whereas at 37° C. there is already the 

 fullest molecular mobility. If now we apply at 30° C. stimuli 

 which increase, say, in arithmetical progression, we see that by 

 the very reception of the increasing stimuli the tissue is made 

 to approach more and more closely to the optimum condition, 

 at which point, as we have seen, the whole of the stimulus is 

 given up immediately, in the form of direct response. Hence 

 the curve showing the relation between stimulus and response 

 in a tissue that is in a condition below the optimum will be 

 steep, and somewhat convex to the abscissa which represents 

 the stimulus ; but at 37"" C, when no molecular sluggishness 

 has to be overcome, we may expect the response to increase 

 proportionately with the stimulus ; that is to say, the curve 

 showing the relation between stimulus and response will now 

 tend to be a straight line. 



In order to apply electrical stimulation whose intensity 

 was increased by known amounts, I used an induction coil, 

 the primary coil of which was completely within the secondary. 

 The ordinary method of Du Bois-Reymond's sliding coil was 

 not very suitable in this case, because the increasing intensity 

 obtained by sliding the coil inwards is merely qualitative. 

 The required definite increase of induction-shock I secured 

 by suitable augmentations in the value of the current that 

 flowed round the primary coil. In order to determine these 

 values, a preliminary experiment was carried out. A storage 

 battery was in circuit with the primary coil, which had 

 interposed in it also an ammeter and a rheostat. By 

 increasing the resistance, a moderate current, say C, read by 

 the ammeter, was adjusted to flow round the circuit. The 

 secondary circuit contained a ballistic galvanometer, which 

 by its throw indicated the intensity of the induced current at 

 make or break of the primar}' circuit. When the first current, 

 C, had given an induced current, which caused a deflection of, 

 say, 30, it was increased to c^, when the deflection due to 

 induction was found to be 50 ; and lastly a third value, or C,^, 

 was found, whose induction-effect was 70. In this manner. 



