EFFECTS OF DRUGS ON PLANTS 



487 



Fig. 200. The Effect of Different 

 Constitutions in Determining the 

 Resistance Offered to Poisons. 

 The Action of 5 per Cent. Solution 

 of Copper Sulphate 



circumstances is made still more striking when we observe 

 the action on the plant of strongly poisonous reagents, such 

 as 5 per cent, solution of copper sulphate. At the normal 

 temperature of 30 C. its application, as will be seen in the 

 record (fig. 200 ), induces a 

 very rapid depression, which 

 soon culminates in permanent 

 arrest. But at 34 C. the 

 resistance offered is consider- 

 able, actually exhibiting it- 

 self in temporary exaltation. 

 At 44 C, again, we observe 

 the poisonous reagent actually 

 initiating growth, as in the 

 last case. 



Opposite effects of the same dose on different consti- 

 tutions. — In the case last considered, we studied the pheno- 

 menon of the resistance offered by the plant to a toxic dose 

 largely in excess of the fatal amount. In spite of the 

 excessive dose we found that, when a favourable constitution 

 was artificially induced, the plant 

 succumbed, it is true, but only 

 after considerable struggle. I shall 

 now proceed to show how, when 

 the artificial constitution is suf- 

 ficiently favourable, the plant, 

 instead of succumbing to an 

 ordinarily fatal dose, can shake off 

 the effect, and may even be stimu- 

 lated by it. Thus I found that a 

 1 per cent, solution of copper 

 sulphate induces depression and 

 is ultimately fatal at 30 C. ; but 



when the same dose is applied to a plant at 34 s C. the effect 

 is seen in a marked exaltation (fig. 201), which continues for 

 a fairly long period, after which it shakes off the effect of the 

 poison altogether, and resumes its normal rate of growth. 



Fig. 201. The Effect of Favour- 

 able Induced Constitution in 

 Enabling Plant to Shake off 

 Result of Toxic Dose of 

 Copper Sulphate 



