THE AUTOMATIC RECORD OF GROWTH 157 



dose of application, which had hitherto not been taken 

 into account. Thus Bose found that while a particular 

 intensity of electrical current accelerated growth, any 

 excess above a critical point retarded it. The same was 

 true of chemical stimulants. A striking practical result 

 was obtained with certain poisons which in normal doses 

 killed the plant, but in quantities sufficiently minute 

 acted as an extraordinarily efficient stimulant, the treated 

 plants growing far more vigorous and flowering much 

 earlier. The treated plants, moreover, successfully resisted 

 the insect blights. Such facts lead to the inquiry into 

 the critical point at which depressant passes into a stimu- 

 lant, or conversely. At this point we see how a fresh line 

 of research has here been opened for Pharmacology and 

 Medicine. And similarly another for speedily testing the 

 action of manurial agents, and other means of accelerating 

 growth for Agriculture. The immediate test needs only a 

 few minutes instead of a season, while the changing con- 

 ditions of the latter are avoided. 



Very striking also is the personal equation of the given 

 plant, i.e. its permanent ' constitution ' and its changing 

 ' tonus.' The latter is found to be experimentally modifi- 

 able. Thus a given batch of similar seedlings was divided 

 into three groups : one was kept normal for reference, 

 another depressed by less favourable temperature to a 

 sub-normal condition, and the third put in an optimum 

 condition. The small dose of poisons which the normal 

 plants could just survive after a period of struggle was 

 found to produce immediate death in the sub-tonic speci- 

 mens ; but the same dose actively stimulated and exalted 

 the growth of the super-tonic ones. Here, again, suggestive- 

 ness for medicine and for agriculture will be manifest. 



The most perplexing phenomena in the life of plants 

 are the ' tropic movements/ which will be described in a 

 subsequent chapter. They are generally brought about by 

 the action of the environment inducing slight modifications 



