172 BOTANICAL GAZETTE [march 



Method 



In order to obtain constant temperatures for heating the seeds, 



rmostat 



It consisted of an 



external water bath heated by an electric stove. In this bath was 

 placed a similar vessel of smaller dimensions which was closed at 

 the top and connected with a water-cooled reflux condenser. 

 Methyl or ethyl alcohol or mixtures of methyl or ethyl alcohol 

 with water was used for temperatures 64-99 C. The tempera- 

 ture during the time of an experiment showed a fluctuation of less 

 than =±=o?i C. For lower temperatures, where the time was much 

 prolonged, the usual water-jacketed incubator was used. This 

 was well wrapped with heavy woolen blankets. The temperature 

 of the incubator was regulated by the automatic electric apparatus 

 devised by Land (21). It gave a very equable temperature, 

 showing a straight line on the drum of an ordinary recording 

 thermometer. 



The seeds were heated in the thermostat by inserting securely 

 corked test tubes, each containing 100 selected seeds, through 

 perforations in the top of the inner vessel. These test tubes were 

 suspended by threads passed through the perforations, and the 

 threads were then secured by corks which closed the openings. 



Many of these tubes were inserted at the same time and removed 

 in duplicate at successive intervals. Seeds were heated in the 



in which k 2 is the rate of reaction obtained at temperature t 2 , and 

 ki the rate of reaction obtained at temperature h. 



Many processes in living organisms show a temperature coeffi- 

 cient approximately that of the Van't Hoff law within certain 

 temperature limits. Some of these show high values of Qi at 

 lower or at critical temperatures. High values of Q I0 are found f 



also for life duration and for coagulation or denaturing of proteins. 



Kanitz (20) brings out more clearly the relation of tempera- 

 ture to the rate of life processes by recalculating Q I0 at the various 

 temperature intervals instead of giving only the average coefficient 

 for the whole temperature range. In this way it is found that in 

 many cases Qi is not a constant at all intervals of temperature, 

 but shows decreasing values with rise of temperature. 









- 



