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Transactions of the Royal Canadian Institute 



the maximum absolute rates were reached usually as late as 17 to 19 hour. 

 The evidence indicates rather clearly, however, that another, lower 

 maximum is previously reached, namely at about the 14 hour. During 

 the period between 14 and 17 hour a second slackening of rate occurs. 

 This behaviour is discoverable on days of sunshine at both normal and 

 supranormal temperatures (table 3; fig. 6). It is to be noticed further- 

 more that the acceleration of growth after 10 hour is greater than on 

 foggy days, and greater at supranormal than at normal temperatures 

 on sunny days. It seems therefor that the accelleration of rate is pro- 

 portional to the amount of shrinkage, and that the time at which it 



/four 8 



Figure 6. Average hour rates of growth for days of continuous sunshine (curve 1), for similar days 

 with high temperatures (curve 2), and for days of continuous high fog (curve 3), (Table 1). 



occurs fluctuates with the time of shrinkage — the earlier the latter, the 

 earlier the recovery. On foggy days a single maximum at i6 hour is 

 approached steadily, and there is no evidence that an afternoon period 

 of slackened growth occurs, as on sunny days. The absolute high rate 

 values on sunny days are uniformly som.ewhat greater than on foggy 

 days, except when higher temperatures prevail when they are consider- 

 ably lower during the period following the first maximum. 



As maturity of the intemode approaches, the zone of elongation 

 becom.es shorter and the absolute values of both shrinkage and growth 



