202 



CONTROL MECHANISMS IN CELLULAR PROCESSES 



in rate is clue to temperature dependence of plasticity (viscosity is 

 temperature dependent, but not usually with as large a temperature 

 coefficient as seen here), which would be an instantaneous effect. 

 In this case we should expect the depression of metabolism, due to 

 decrease in temperature, to exert itself as a further decrease in 

 growth rate as the metabolism-dependent plasticity decays to a de- 

 pressed value, and we should also see a further increase in rate 



20 



40 



60 

 TIME MIN. 



80 



100 



120 



Fig. 7-1. Effect of changing the temperature from 23" to 12° C {first arrow) 

 and back to 23° C {second arrow) on growth of an oat coleoptile section 9 mm 

 long, in 3 mg per liter indoleacetic acid. The same changes of temperature were 

 repeated at subsequent arrows. 



after the initial effect when the temperature is raised. Subsequent 

 to the initial change in rate there was, if any change, only a tend- 

 ency for the rate to recover somewhat at the lower temperature ( for 

 example in the first 12° treatment in Fig. 7-1) or to fall slightly at 

 the higher temperature, which effects we know were not due to cor- 

 responding changes in temperature since temperature was followed 

 throughout. 



There remains the possibility of a "deepfreeze effect," that the 

 connection between metabolism and plasticity has such a long-time 



