625 



heat. Grapevines, roses, etc., are covered with earth or leaves, or the 

 trunks are wrapped in moss, straw and the like. All these means are good 

 but in cold winters, with a moderate snowfall, one should not delay throw- 

 ing the snow from the streets on to the covered plants. It is well known 

 that wrapped tnmks of roses, for example, often freeze; this is explained 

 by investigating the temperature under the covering material with a ther- 

 mometer. It is found to deviate but little from the temperature of the outer 

 air. On the other hand, if the soil under the snow covering, possibly 15 cm. 

 deep, is investigated, it is found to be considerably warmer. Goppert's 

 investigations^ are the best on this subject. In February, 1870, the tempera- 

 ture was very low. The thermometer fell on the 4th to 12.6 degrees below 

 zero, on an average, and yet in this, the temperature was only 3 degrees 

 below zero under the snow covering, 10 cm. deep. The temperature of 

 the air 



on Feb. 5 was 14 7 degrees below zero, the temperature under the snow 4.6 degrees 



below zero, 

 on Feb. 6 w-as 17.6 degrees below zero, the temperature under the snow, 5 degrees 



below zero, 

 on Feb. 7 was 16.7 degrees below zero, the temperature under the snow, 5.5 degrees 



below zero, 

 on Feb. 8 was 16.7 degrees below zero, the temperature under the snow, 6.5 degrees 



below zero, 

 on Feb. 9 was 15 4 degrees below zero, the temperature under the snow, 6 degrees 



below zero, 

 on Feb. 10 was 14.9 degrees below zero, the temperature under the snow, 6 degrees 



below zero, 

 on Feb. 11 was 15.8 degrees below zero, the temperature under the snow, 5 degrees 



below zero, 

 on Feb. 13 was 5.7 degrees below zero, the temperature under the snow, 2 degrees 



below zero, 

 on Feb. 16 was 2.8 degrees below zero, the temperature under the snow, 1.5 degrees 



below zero. 



The soil under the snow covering was frozen 36 cm. deep, but its tempera- 

 ture, even on the cold 5th of February, at a depth of 5 cm., was only one 

 degree below zero. 



It would scarcely be possible to find more eloquent proof of the useful- 

 ness of a snow covering. This explains the possibility of polar vegetation. 

 The greatest degrees of cold in the polar zone as yet observed (40 to 47 

 degrees below zero) affect only the trunks of the trees which project above 

 the snow, but not the roots. Perennial, herbaceous plants are just as little 

 afifected. These stand in a soil with a temperature under the snow cover- 

 ing of only a few degrees below zero. The snow covering, to be sure, does 

 not arrest freezing but does prevent loss of warmth through radiation, the 

 penetration of greater degrees of cold and a rapid change in temperature. 

 But, even with us, the existence of many plants is more often connected 

 with snow covering than we think. The freezing of seed would occur 

 much more frequently when a long damp and moist autumn favors plant 

 development, if the snow covering were not deposited on them, which keeps 

 off radiation and the great fluctuations in temperature, so frequent in our 

 latitudes. We see often enough how easily insufficiently protected, or fully 



1 Bot. Zeit. 1871, No. 4, p. 54. 



