220 Transactions of the Royal Canadian Institute 



dawn till 7 or 8 hours, (3) the reduction of rates till about 10 hour, 

 (4) the rapid increase thereafter till the 15 or 16 hours, and (5) the final 

 drop to the night rate. The absolute values for any day depend largely 

 on the degree of development already attained by the internode. Ob- 

 viously, when it has almost completed its growth, the amount of growth 

 relative to the extent of the growth zone may be as great as before 

 although in absolute terms it is much reduced. Having due regard to 

 this fact, however, the records show that no single day out of 53 for 

 which complete hourly records were obtained failed to display this behaviour. 

 It will, however, be pertinent and necessary to point out the departures 

 from the average behaviour. Their extent is shown sufficiently well by 

 the graphs in figure 4, which are the average hourly rates for the several 

 internodes treated separately. The following statements are based on 

 a study of all the data, some of which, however, as above said, have 

 been omitted from this paper. 



Night growth rates : There was almost invariably a gradual drop 

 in rate during the hours preceding midnight, during which period also 

 there was a reduction in air temperatures. Between midnight and 

 4 hour the rate was quite constant, having an absolute value of .1 to 

 .2 mm. per hour. A maximum rate of .4 mm. per hour was observed 

 once, while, in internodes approaching their limit of growth, there 

 might be practical cessation of growth. The behaviour after midnight 

 did not seem to follow air temperatures alone, since the minimum 

 temperatures were usually reached at from 4 to 6 hour. In only four 

 instances was minimum growth recorded for 6 hour, while the minimum 

 temperatures occurred at this hour 26 times during the period of obser- 

 vation. 



From 4 to 6 hour, the period of dawn, there was still b it little growth, 

 there having been recorded a slight increase of rate on half the days of 

 observation, the rate on other occasions having remained constant 

 except on four days when in long internodes there was a slight fall in 

 rate. This occurred on mornings when the temperatures rose rapidly, 

 but did not involve an absolute change of rate of more than .2 mm. and 

 was followed by rise for a brief peroid. 



After the 6 hour the rate remained either constant, or more usually 

 rose somewhat, the rate increase being somewhat greater on foggy days. 

 On about 25% of the days it fell. That is to say, the period of shrinkage 

 might set in as early as 6 hour, but the turning point was usually later, 

 generally at 7 hour; and it might be as late as 9 hour. The maximum 

 rate, in 96% of the instances was not more than double the minimum 

 night rate. In one instance a rate thrice, and in another, nearly five 

 times that of the minimum night rate was attained (on S. 4). The 



