EFFECTS OF DRUGS ON PLANTS 



481 



In b is shown the effect of an internal application, made by 

 replacing the water, by which the cut end of the stem was 

 normally surrounded, with a 3 per cent, solution of ether. 

 It will be seen that, as the specimen sucked up the solution, 

 the immediate effect of this 

 internal application was an 

 enhancement of the rate of 

 growth, and that this was 

 followed by depression, lead- 

 ing to arrest of growth. The 

 preliminary depression seen 

 in a is thus wanting in the 

 case of the internal applica- 

 tion. It might be thought 

 that this first depression, as 

 seen in the case of the ex- 

 ternal application, was due to 

 a slight cooling, caused by 

 the introduction of ether. We 

 know, however, that while 



lowering of the temperature, as long as that is below the 

 optimum, would suffice to retard growth, a similar lowering 

 of it when above the optimum would have the opposite effect 

 of acceleration. Now I find that 

 this preliminary retardation of growth, 

 seen in fig. 193, a, takes place in 

 exactly the same manner when the 

 experiment is repeated with the 

 specimen at 38°C. It cannot, there- 

 fore, be due to the suggested cooling, 

 which must in any case, under the 

 experimental conditions, have been 

 extremely slight. There is, however, 

 another explanation, which more nearly meets the require- 

 ments of the case. We know that any sudden variation of 

 environmental conditions is apt, generally speaking, to act as 

 a stimulus, and the effect of direct stimulation is always to 



I I 



Fig. 193. Balanced Records oi 

 Effect of Ether on Growth. Up 

 Curves represent Acceleration 

 Above, and Down Curves Re- 

 tardation Below, the Normal 



a Effect of external application, and 

 /; of internal application of ether. 

 Successive thick dots in the base- 

 line indicate time in minutes in 

 this and following records. Arrow 

 shows moment of application. 



Fig. 194. Excitatory Effect 

 of Dilute Solution of So- 

 dium Carbonate on Growth 



