50 chap. v. effect of chemical agents 



Summary 



The effect of a chemical agent on growth is determined 

 by the strength of the dose, the duration of appHcation, 

 and the tonic condition of the tissue. A poisonous substance 

 in minute doses often has the effect of enhancing the rate 

 of growth. 



The effect of any chemical agent on various growing 

 organs, such as the stem, the petiole, the flower-bud, and 

 the pistil, is essentially the same. 



The various anaesthetics induce more or less similar 

 reactions on growth ; of these carbonic acid gas may be 

 regarded as a mild and chloroform as a strong anaesthetic. 



Carbon dioxide induces a preliminary enhancement of 

 the rate of growth ; its continued action is followed by 

 decline and arrest of growth. The influence of CO2 is the 

 same in darkness as in light, the effect being thus inde- 

 pendent of photosynthesis. 



A small dose of ether induces a great enhancement in 

 the rate of growth ; a large dose paralyses growth, but 

 timely substitution of fresh air is followed by revival. 



The effect of continued action of chloroform vapour on 

 growth is as follows : at the first stage there is acceleration ; 

 at the second stage growth becomes arrested ; at the third 

 stage there is a violent contraction which is the spasm of 

 death. 



A small dose of ether or chloroform renews growth which 

 had previously been in a state of standstill. This no doubt 

 explains the action of these anaesthetics in forcing growth 

 of dormant buds in winter. 



Sulphuretted hydrogen retards growth and acts as a 

 poison ; the effect of ammonium sulphide is similar. 



Copper sulphate, in minute doses, often has the effect 

 of enhancing the rate of growth. A stronger dose, or 

 a prolonged action, however, induces a depression which 

 culminates in the death of the plant. 



