228 Transactions of the Royal Canadian Institute 



higher temperatures. For the following period of two hours the balance 

 is the other way, to change again later. At the hours therefore of 

 maximum insolation the absolute hour rates are on the whole higher on 

 sunny days. 



Again, if we take the total amounts of growth during the hours of 

 daylight following the last minimum rate, for the different days, we 

 find that for sunny days the average total growth is 4 mm., for such 

 days with higher temperatures, 4.6 mm., and for foggy days 4 mm. By 

 discarding extreme figures we find but little difference in the final ex- 

 pression, so that we may conclude that the general result of growth 

 performance does not indicate less favourable conditions to be due 

 merely to sunshine. 



The record for August 8th to 20th bears out this conclusion. These 

 were days of continuous sunshine save for fog after the critical hours, 

 as indicated in figure 8, on August 13th and 14th. The maximum 

 total growth occurred on a day of continuous sunshine (August nth) 

 with moderate temperatures. August 12th, 15 and 16 were days of 

 equal amounts of growth. On the 12th the part was subjected to high 

 temperatures of a closed chamber, and the light was intensified by means 

 of mirrors, the window being of uviol glass. Somewhat lower, but still 

 high temperatures obtained on the 15th and i6th, with blue light on 

 the 15th and red on the i6th. Consonant with the high temperatures the 

 higher daily growth rates {e.g., as compared with August nth) were 

 delayed till after the noon hour, and this delay was especially noticeable 

 on the 1 2th, when the temperatures of the chamber reached, and were 

 sustained at, abnormally high quantities. Indeed, the possibility of 

 interpreting the depression of growth on this day as due direcdy to 

 the intense illumination as such is admitted, but is excluded by other 

 evidence, as e.g., the sudden increase of rate to a high value under the 

 same conditions of illumination merely by raising the humidity (July 

 i6th, 17th); and the high rates on August 24th, the increase beginning 

 at 10 hour and reaching a maximum of 15 hour. When one reflects 

 that the conditions supplied to the growing part on August 12th were 

 most stringent — much more so than would ever occur in the habitat 

 where these experiments were done — it is a matter of surprise that the 

 rates of growth were as high as recorded. 



EXPERIMENTAL. 



Transpiration. — The transpiration rates of two plants were deter- 

 mined synchronously, together with evaporation rates. Of the plants, 

 one retained its rosette of leaves; from the other they were removed. 



