SOME EFFECTS OF SEVERE FROST UPON VEGETA- 

 TION IN A CONDITION OF ACTIVE GROWTH. 



Frederic K. Butters and C. Otto Rosendahl. 



Introduction. 



The spring- of 1910 was exceedingly early in Minnesota. 

 Following a winter with heavy early snowfall and almost no 

 frost in the ground March was 6 degrees (C) warmer than 

 usual — about the temperature of a normal April. There were a 

 few cool nights about April 1st, but no frost and the next ten days 

 were entirely summerlike. 



The result was that by April 15th vegetation was as far ad- 

 vanced as it is usually in late May. and was growing very 

 rapidly without having received any check whatever. Fruit 

 trees were in full bloom or a little past their prime. Many of 

 the forest trees were in leaf, others were just leaving out and 

 growing rapidly. Much of the earliest herbaceous vegetation 

 was through flowering (e.g. Sanguino/ria, Hepatica) and develop- 

 ing its fruits, while many of the slightly later herbs were at 

 the maximum of flowering. 



On April 15th it began to freeze a little before midnight and 

 about sunrise of the 16th reached a temperature of -2.7° C (27° 

 F.). Somewhat less intense frost occurred on the two following 

 nights. During the intervening days the temperature rose a few 

 degrees above freezing. The weather was cloudy and on the 

 afternoon of the 16th about two inches of wet snow fell, re- 

 maining on the ground and on vegetation until the morning of 

 the 18th. This period, April 15th to 18th, will be spoken of 

 collectively as the "first frost." Nearly all the damage to vegeta- 

 tion occurred during the night of April 15th. The slightly higher 

 temperature of the following nights in connection with the cover- 

 ing of snow produced almost no injury to vegetation which had 

 survived the frost of the first night. 



