44 The Ottawa Naturalist. [May 



temperature, so that 1902 would naturally retain its lead. But the 

 last four days of this month were on an averag-e considerably 

 warmer (6.7*^ per day) in 1903, and this continued the case through- 

 out the two following^ months except in the second part of June. 



It was in the closing" days ot April, therefore, that 1903 be- 

 gan to gain on 1902, and the rapidity with which it overtook and 

 passed 1902 is readily explained by a comparison of the tempera- 

 tures in May. During the first five days 1903 was only warmer 

 by 1.4° per day. but during the next five days by 18*^ per day ! 

 It was evidently during those five remarkably warm May days 

 that the vegetation of 1903 overtook that of 1902. During the 

 second third of May the days were 16" warmer than in 1902, or 

 almost as much warmer as during the second five days, thus 

 accounting for the remarkable spurt in vegetation in the middle 

 of May, 1903, which my observations showed to exist. That last 

 season's lead should have continued and even increased in the last 

 third of May, is again explained by the fact that the daily maxi- 

 mum temperature during this period was higher in 1903 by .5°. 

 But, although the temperature was still warmer in the first part of 

 June, 1903, as compared with 1902, by 9°, yet there was a falling 

 oflr of one day in the lead of the vegetation of 1903. Some other 

 controlling factor seems to have operated here. During the 

 middle part of June the maximum temperature of 1903 was less>. 

 than that of 1902 by 4° per day. This change is indicated by my 

 observations, which show a lead of eight days during this ten day 

 period as against nine for the previous period. 



The daily minirmini temperature, though of course not so 

 good an index of plant growth, yet tells in a general way the 

 same story. In both the years under consideration the average 

 minimum daily temperature wa'J below the freezing point up to 

 and including the 6th April. After that date there were only five 

 days in 1902 when the minimum fell to or below 32*^, the last time 

 being the 1 ith of May;"* whereas in 1903 this occurred fifteen times, 



* It migfht be pointed out in tliis connection, that, as the flow of the maple 

 sap throug-h the tap-hole is dependent upon the fluctuation of the temperarure 

 above and below the freezing; point, or 32° F., the sug-ar season around Ot- 

 tawa must have practical!}' ceased on the 6th April in 1902. 



