It will thus be seen that, in the course of an experiment lasting about twenty minutes, data have been obtained which enable us to determine the rates of growth through a wide range of temperature. We have likewise been able by the first method to make very accurate determinations of the temperature maximum and minimum. In short, by adopting the methods described, the cardinal points of growth and the rate of growth at any temperature, may be determined with a precision unattainable by the older methods, of averages or of prolonged observation. SUMMARY. Temperature induces variation in the rate of growth. In accurate determination of the growth, the disturbing effect of radiation of heat has not been eliminated. A continuous record of growth under uniform rise of temperature gives the Thermo-crescent curve, from which the rate of growth at any temperature may be deduced. Different plant-tissues exhibit characteristic differences in their cardinal points of growth. In _Kysoor_, growth is arrested at the temperature minimum of 22°C. The optimum temperature is at 34°C., after which growth-rate declines and becomes completely arrested at 58°C. At 60°C. there is a sudden spasmodic contraction of death. In other plants the cardinal points are different. In some plants the optimum growth is attained at 28°C. and remains constant up to 38°C. XII.--THE EFFECT OF CHEMICAL AGENTS ON GROWTH _By_ SIR J. C. BOSE, _Assisted by_ GURUPRASANNA DAS. Chemical agents are found to exert characteristic actions on growth. The method of investigation sketched here opens out an extended field of investigation. The effect of a chemical substance, I find, to be modified by (1) 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 reactions.