CHAPTER XXXV 



AN INVESTIGATION INTO THE DIFFERENT EFFECTS OF 

 DRUGS ON PLANTS OF DIFFERENT ' CONSTITUTIONS ' 



General consideration of the problem — ' Constitution ' and the elements which 

 determine it — Methods of investigation— Action of carbonic acid gas — Action 

 of ether — Effect of solution of sodium carbonate — Effect of solution of sugar — 

 Effect of alcohol— Effect of acids — Effect of alkali — Antagonistic action of 

 alkalis and acids — Action of strong solution of sodium chloride — Effect of 

 poisonous solution of copper sulphate — Opposite effects of the same dose on 

 different constitutions — Opposite effects of large and small doses. 



We have already studied the effect of various chemical 

 agents on the physiological condition of plants, as seen 

 from the modifications induced by them in ordinary and in 

 autonomous responses. We have also noticed the remark- 

 able similarity between these effects in the two cases of 

 plant and animal tissues, and I have drawn attention to 

 the great practical utility of these investigations, inasmuch 

 as the experiments carried out on plants may be made 

 to throw light on many obscure phenomena regarding 

 the effects of drugs on the animal system. One puzzling 

 fact, however, which is encountered in medical practice, is, 

 that the same drug will often produce varying effects on 

 different individuals ; and this is vaguely ascribed to dis- 

 similarity of ' constitution.' 



Similarly, we have sometimes seen different effects to 

 occur in plants under the action of a single given drug. 

 A large dose of some depressing agent, for example, though 

 it will ultimately produce the depressing effect, will not 

 always do so at once, for in some cases there will be a pre- 

 liminary period of exaltation of response. The same toxic 

 dose, again, which will in some instances kill the plant, will 



