Page:Life Movements in Plants.djvu/217

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CHEMICAL AGENTS ON GROWTH
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the rate from 0.45 μ to 0.13 μ 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 acceleration of growth.

The action of dilute vapour of ammonia is a preliminary enhancement followed by depression of growth.

Ether vapour depresses the rate of growth. On the removal of the vapour there is a recovery of the normal rate.

The effect of carbonic acid is a great enhancement of the rate of growth; after this preliminary action, growth undergoes a decline. The effect described takes place equally in light or in darkness.

Coal gas induces a depression of the rate 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.

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