RELATION BETWEEN TEMPERATURE AND GROWTH 447 



resistance, or vice versa. After a little practice the process of 

 regulation becomes almost instinctive. The record of growth is 

 now taken continuously on the revolving drum, and the thermo- 

 crescent curve obtained under these conditions of continuous 

 variation of temperature is seen to be extremely regular, giving 

 data by which we may determine the rate of growth at any 

 point of the curve (fig. 183). The revolving drum gave, as 

 already said, a movement of the recording surface of 6 mm. per 



Fig. 183. Thermo-crescent Curve of Growth in Crinuiii Lily 

 under Continuously Increasing Temperature 



minute. That length of the abscissa would therefore repre- 

 sent one minute of time ; and since the rise of temperature 

 was regulated, at 1° C. of rise per 2-5 minutes, intervals of 

 15 mm. in the abscissa also represent 1° C. in temperature. 

 With the magnification used, i mm. of the ordinate represents 

 a growth-elongation of a thousandth part of a mm. In order, 

 therefore, to obtain from this curve the rate of growth at any 

 given temperature, say at 34° C, we have to find the elonga- 



