RELATION BETWEEN TEMPERATURE AND GROWTH 445 



represents *ooi mm., the rate of growth is thus "0075 mr n. 

 per minute. The rheostatic handle was afterwards turned to 

 the mark 35° C. With the particular battery power used in 

 this case, the permanent rate of rise to 35 C. was attained 

 after a period of three minutes. It will be seen from the record 

 that the stimulus of sudden variation of temperature caused 

 a contractile twitch, after which 

 growth proceeded at a very 

 rapid rate during the variable 

 period. But as soon as the 

 temperature of the chamber had 

 attained a permanent condition 

 — i.e. 35 C. — the rate of growth 

 became constant. The attain- 

 ment of this constant rate was 

 practically simultaneous with 

 the attainment of the permanent 

 temperature condition. The 

 lag, in any case, if it existed, 

 could not be more than fifteen 

 seconds. 



One curious and interesting 

 fact to be fully explained later, 

 which was noticed in the course 

 of the experiments, was that 

 the amount of contractile twitch 

 went on increasing during the 

 variable period, as the tempera- 

 ture was raised each time i° C, 

 from 30 to 35 C, but after 



this point practically disappeared. The permanent rate of 

 growth, then, at a temperature of 35 C, is, as will be 

 seen from the figure, twenty-four divisions per two minutes, 

 or 'OI2 mm. per minute. In this way, by taking successive 

 records at different temperatures, I obtained the following 

 rates of growth, in the cases of Crinum Lily and the peduncle 

 of Crocus. 



Fig. 182. Record of Growth in 

 Crinum at Temperature of 34 C. 

 and 35 C. 



The dotted line represents the 

 variable period of temperature 

 ^change. Note the contractile 

 twitch and transient highly ac- 

 celerated growth which follows. 

 The rate of growth became con- 

 stant when the temperature be- 

 came permanent at 35 C. 



