

not maintained temperatures they may differ (a) as tc the 

 particular temperatures with which the cultures were started, 

 (b) as tc the direction of variation during a given period 

 (whether the temperature became higher or lower with time), 

 and (c) as to the time rate of temperature variation. It is 

 clear that this rate of change in temperature may itself he 

 constant, or may vary throughout a given time period. When 

 only maintained temperatures are to he considered as in the 

 present study, the only difference to he dealt with between 

 any two cultures are those of degree or intensity as measured 

 in terms of centegrade, etc., degrees. 



(4) Radiation condit ions, involving the various 

 groups of wave-lengths of radiation and the relative and 

 absolute intensities of each group. Up to the present time 

 most biological discussion has ignored most of the wave- 

 lengths of radiation excepting the small group commonly des- 

 ignated as light. Since me cultures of the present study 

 were uniformly carried out in darkness and in chambers around 

 which a mass of water was continuously rotating, radiation 

 conditions will not require attention here. 



(5) The duration cond i tion , implying the length 

 of time during which the organism is subjected to tne other 

 conditions. From one point of view every condition has a 

 duration factor, but when most of the conditions are main- 

 tained, or practically 30, the duration factor i3 common to 

 all, and we may re =.-&.rd it as a separate condition. 'Tore- 

 over, as far as the present in •stigation is concerned this 



