236 Transactions of the Royal Canadian Institute 



Reduction of light was followed by increased rates but these were 

 much inferior to those attained with full illumination after 15 hour 

 when high fog prevailed. The amount of growth for 38 min. was at 

 an hour rate of 2.1 mm., about equal to a recorded amount of growth 

 for an entire hour on August 24th (datum: 2 mm. 14-15 hour). 

 July 15th, see page 31 (fig. 10). 



The efTect of the screen and mirrors was to impose insolation on the 

 otherwise shaded sides of the internode and to raise the temperature. 

 This was done at 8.30 hour when shrinkage was to be expected, but 

 recovery proceeded normally at a very high rate (i.i mm. per hour) on 

 increasing the humidity at 9.49 hour. Reduced light at 10.16 hour per- 

 mitted an increased rate after it had been lowered by reduced humidity. 

 A high fog intervening favoured still higher rates. Change from blue 

 to red was followed by a slight advance in rate for 30 min. when lower 

 rates persisted till 15 hour when they jumped to 65. The greatest 

 change in rate, therefore, occurred during high illumination but induced 

 by raising the humidity. The greatest amount of growth for a sustained 

 period occurred with maximum illumination (sun plus mirrors) during 

 the late afternoon. 



Aug. 26, beginning with 7 hr. reading (fig. 5): 



10 10 10 10 10 



o 120 -60 60 48 



The growth curve for this day was also decidedly irregular from 

 9.30 on and particularly so between 11 and 14 hour. The possibility 

 of instrumental error was appreciated but the character of the night 

 records, which were uniformly smooth, and those for the same internode 

 on other days before and after the 26th, which bore the same character, 

 exclude this possibility. It was, however, a long, slender internode in 

 which irregular growth might well be expected. In spite of reducing 

 the light but raising the temperature in the chamber in the morning, 

 shrinkage occurred. Increase of light at 11 was followed in 10 min. 

 by high rates for short periods with a brief period of shrinkage inter- 

 vening. 



Aug. 27, beginning with 8 hr. reading. Hour periods. 

 Rate: 25 20 10 o blue screen at 11 -20 45 xo 27 63 60 60 17 



Reducing the light did not induce more rapid rates of growth nor 

 were the rates at the time of normal most rapid growth as high as they 

 sometimes were with full insolation, e.g., on August 24th (table 3). 



