

60 ANNALS OF THE MISSOURI BOTANICAL GARDEN 



[Vol. 2 



ous covering of ice, which destroyed all vegetation except 

 perhaps the most hardy. All other species of plants have 

 immigrated subsequently from the neighboring countries, 

 which were not covered with ice during the Glacial Epoch, 

 and could therefore afford a dwelling-place for a more or 

 less abundant flora. 



In the following pages I shall endeavor to give an account 

 of the results at which historical phytogeography may be said 

 to have arrived as far as Norwav is concerned. 



Survey of the Distribution of the Norwegian Flora 



It will first be necessary, however, to give a general ac- 

 count of the most important points regarding the composi- 

 tion and distribution of the Norwegian flora throughout the 

 country. I shall here consider only the vascular plants (about 

 1,500 species), however, as the distribution of the lower 

 plants is not sufficiently known to enable us to draw definite 

 conclusions. 



The area of Norway is about 125,000 square miles, stretch- 

 ing from latitude 57° 58' 43" north to latitude 71° 10' 20" 

 north. The conditions for plant life will thus be very differ- 

 ent in the southern and northern parts of the country. But 

 in addition to this, there is a great difference between the 

 climate in the east and that in the west of southern Norway. 

 In the valleys of the East Country, there is a very pronounced 

 inland climate, with hot summers and a winter temperature 

 that falls below — 40 °C, while on the west coast region there 

 is a low summer temperature, but a mean January tempera- 

 ture of sometimes more than 2°C. 



The most important condition affecting the distribution of 

 plants in Norway is the temperature. In this connection we 

 shall in the first place speak of the lowest winter tempera- 

 ture that the plants can survive. J. Hohnboe ('13) has 

 shown that the distribution of Ilex a qui folium in Norway 

 coincides closely with the January isotherm for 0°C. Herb- 

 aceous plants which die down in the winter may of course be 

 independent of the lowest winter temperature, as they are 

 covered with snow; but they are not entirely independent of 



