Page:Life Movements in Plants.djvu/212
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 be 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.