1915] 



WILLE FLORA OF NORWAY 



61 



the spring and autumn temperature. Plants are also in a 

 great measure dependent on the height of the temperature in 

 the period of vegetation, which, in Norway, comprises in the 

 main the four months, June, July, August, and September. 



Fig. 1. 



Isotherms for January. 



In this way, the conditions prevailing in Norway are very 

 varied, the July isotherm for Christiania being 17 °C, while 

 for the west coast it is only from 12 to 14° C. 



A. Helland ('12) has calculated that where the mean sum- 

 mer temperature in Norway is less than 13° C, the fruit 



