the rate from 0'45 ,1 to 0'13 a per sec. Long continued action
of the poisonous solution kills the plant.
SUMMARY.
The effect of 'a chemical agent is modified by the strength of the solution, the duration of application and the tonic condition of the. tissue.
Dilute solution of hydrOgen peroxide. induces an accele- ration of growth.
The action of dilute vapour of ammonia is a prelimin- ary enhancement followed by depression of growth.
Ether vapour depresses the rate of growth. On the re- moval of the vapour there is a recovery of the normal rate.
The ell‘ect of carbonic acid is a great enhancement of the rate of growth; after this preliminary action, growth undergoes a decline. The eli'ect described takes place equally in light or in darkness.
Coal gas induces a depression of the mic of growth from which there is a recovery after the. removal of the gas. The action of sulphuretted hydrogen is far more toxic, the after-effect being very persistent.
Solution of ammonium sulphide induces increasing retardation of growth, with the strength of the solution. Copper sulphate solution acts as a toxic agent, retarding the rate of growth and ultimately killing the plant.
