duration condition may be divided into two partB, each one of 

 which may be considered as a sepc.aite condition : (a) The 

 actual length of any interval of tine being considered, and 

 (b) the location of this time interval serially in the ent 

 culture period reckoned from its beginning. If the time 

 period is always reckoned from the beginning then the second 

 part of this duration condition may be neglected and only the 

 length need be considered, as is done in tne first part of 

 tne discussion of the present investigation. When, however, 

 changes In rate of growth with time are being studied, che loca- 

 tion of the time interval as well as its length come to be 

 important, and these may be regarded as two iifferent condi- 

 tions and this is done in the latter part of the discussion. 

 To illustrate these further, a certain fungus, Pythiacystis, 

 (condition l) , is surrounded by nutrient agar (condition 2) 

 and subjected to a maintained temperature of 23° C (condi- 

 tion 3) in darkress (condition 4) and it exhibits a growth 

 rate of 7.8 mm. per day for a period of two days (condition 

 5) when this period is, in relation to the initial moment of 

 exposure, the first (condition 6). If this experiment ie 

 repeated with everything the same excepting that condition 

 5 (tne length of the observation period) is the first 3 day 

 period instead of the first two day period, then tne mean 

 growth rate per day is 3.0 mm. which is markedly different 

 from that shown in the first case. 



the examples just given the observation periods, 

 though of different lengths, had the same relation to the 



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