Page:Life Movements in Plants.djvu/212

182 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 prezision unattainable by the older methods, of averages or of prolonged observation.

Temperature indoor-s variation in the rate. of growth. In accurate determination of the growth, the disturbing etl'ect of radiation of heat has not. be eliminated.

A continuous record of growth under uniform rise of temperature gives the 'l‘hernui-cresCent curve, from which the. rate. of growth at. any temperature may be deduced.

Different plant-tissues exhibit characteristic ditl'erences in their cardinal points of growth. In Kysoor, growth is arrested at the temperature minimum of 22°C. The. optimum temperature is at. 31°C., after which growth-rate declines and becomes completer arrested at 58°C. At 60°C. there is a sudden spasmodic Contraction of death.

In other plants the cardinal points are ditl'erent. In

~some plants the optimum growth is attained at 28° C. and remains constant up to 38° C.