460 



PLANT RESPONSE 



the direct effect was a retardation of 31, which was followed 

 by an augmentation of 14 divisions. Thus the sum of these 

 two effects is practically constant, being in one case 46, and 

 in the other 45, divisions. 



Constancy of sum of direct effect and indirect after- 

 effect. — This constancy, however, becomes still more remark- 

 able when the same plant is raised to a temperature of 35 C. 

 and subjected once more to the same stimulation. The direct 

 effect is now shown by a retardation which may be repre- 

 sented as 39, and the in- 

 direct by 9, divisions. In 

 the second response of this 

 second series, we have a 

 direct effect of 37, and an 

 indirect effect of 8, divi- 

 sions. Thus the sum of 

 the first direct and indirect 

 effects is 48, and the sum 

 of the second 45, divisions, 

 the mean of the two at 

 35° C. being 46-5 divisions, 

 while the mean at 30 C. 

 was 45*5 divisions. We 

 have found, then, not only 

 that the sum of direct and 

 indirect effects at a given 

 temperature is practically 

 constant when stimulus is the same, but also that this sum 

 itself remains approximately constant at different tempera- 

 tures within the optimum ; and, further, we see that as the 

 excitability is increased in approaching the optimum, the 

 direct effect also increases at the expense of the indirect. 

 In other words, when the tissue is at its optimum tonic 

 condition, its capacity for the absorption of stimulus being 

 already fully satisfied, the external stimulus tends to be 

 immediately expended, in direct response, allowing relatively 

 little to become latent. 



Fig. 185. Series of Responses of Growing 

 Organ of Crinum Lily, taken under 

 Balanced Conditions at Three Different 

 Temperatures 



On comparing these records it will be seen 

 that the direct effect increases up to 

 the optimum, and that the indirect 

 effect of accelerated growth decreases. 

 Beyond the optimum, at 37 C, there 

 is no latent component, as shown by 

 recovery from direct effect to normal 

 rate of growth. 



