I lO 



Journal of Agricultural Research 



Vol. Ill, No. 



growth. The extent of this influence is shown in figure 4. It will be 

 observed that freezing temperatures occurred on three nights in July, 



1909 — namely, July 12, 17, 

 and 27 — the temperatures 

 recorded being 30°, 23°, 

 and 29° F., respectively. 

 In August freezing tem- 

 peratures occurred on the 

 ist, 4th, 2oth, and 26th, 

 the lowest being on the 

 night of the 4th, when the 

 temperature registered 28° 

 F. Only on the nights 

 of freezing temperature in 

 July, however, was serious 

 harm done, and then only 

 to the young seedling 

 plants. The greatest in- 

 jury occurred on the more 

 moist, but not marshy, 

 situations, where the sur- 

 face soil heaved as a re- 

 sult of alternate freezing 

 and thawing. This action 

 of the soil exposed por- 

 tions of the roots of the 

 seedlings, leaving them at 

 the mercy of the sun and 

 wind. In a few excep- 

 tional cases 50 per cent of 

 the seedling stand was thus 

 destroyed. The freezing 

 temperatures during Au- 

 gust were not destructive, 

 since then the root systems 

 were better developed and 

 there was less heaving of 

 the soil, on account of the 

 lower moisture content of 

 the surface layer. 



Because of the high el- 

 evation of the Hudsonian 

 zone, the maximum tem- 

 perature rarely exceeds 90° F. and, as a rule, does not seriously 

 hamper the activities of the vegetation, though, in so far as it influences 



