220 Jhhitioii^ iH'tirrcn Grotrfli (uhJ EHVironniritt 



If these figures are appropriately grouped it is seen that the length of 

 the first period bears a direct relationship to the range of the mean weekly- 

 maximum temperatures; the time decreasing witli the rise of the mean 

 maxima. On the other hand the range of the mean minimum temperature 

 seems of little significance as the variations are very irregular and do not 

 run parallel with the length of the first period of growth. 



It is thus evident that the rate at which assimilation is able to make 

 good the loss by respiration increases directly with rise of temperature; 

 at the lower temperatures a very small increase will reduce the period 

 by a week or more, but higher up the scale a slowing off in the time 

 reduction is noticed. It is probable that this is really a temperature effect 

 rather than one due to light intensity, for with similar temperatures the 

 same length of 1st period growth occurred at different times in the year, 

 e.g. in series M started on April 26th the period of two weeks was the same 

 as in series Q started on October 3rd, though the light intensity in the 

 first case would probably be greater than in the second, while 68-2 hours 

 of bright sunshine were recorded in the April period and only 12-1 hours 

 in the October period. 



The initial stage of growth, therefore, is represented by a period 

 during which the weight lost by respiration is made up by a gain due to 

 the beginning of assimilation, the rate at which this compensation occurs 

 depending on the maximum temperature. 



2nd period of growth. 



All the series behaved in a similar way during the first period except 

 with regard to the length of time that this persisted. The second ])eriod, 

 that of active growth, is very different, and each series presents its own 

 individual characteristics. Analysis of the results obtained, however, 

 show that these characteristics bear a clear relation to the variable 

 factors at work, and that the plant responds definitely and not arbitrarily 

 to change in the environmental conditions. 



