Page:Life Movements in Plants.djvu/213

 Chemical agents are found to exert characteristic actions on growth. The method of investigation sketched here opens out an extended field of investigation. The oll'ect of a chemical substance, I find, to be modified by (I) the strength of the solution, (2) the duration of application, and (3) the condition of the tissue. A poisonous substance in minute doses is often found to exert a stimulating action. Too long continued action of a stimulant, on the other hand, exerts a depressing effect. The inﬂuence of the tonic condition is shown by the fact that while a given dilution of a poisonous substance kills a weak Specimen, the same poisonous solution, applied to a vigorous specimen, actually stimulates and enhances the rate of the growth. I give below descriptions of a few typical re- actions.

The reagent, when in a liquid form, is locally applied on the growing organ. The records, taken before and after the application, exhibit the stimulatory or depressing character of the reagent. A different method of application of the reagent is employed for plants with extended