THE FLORA OF NORWAY AND ITS IMMIGRATION 



N. WILLE 

 Professor at the Christiania University 



The phytogeographical investigations in a country may be 

 carried on in the following three main directions : 



Floristic phy to geography, or an investigation into the geo- 

 graphical distribution of the plant species. The result of this 

 work should be charts of the distribution in the country of 

 the various species. In a country with such varied condi- 

 tions of life as Norway, this is a very comprehensive and 

 very arduous task, requiring an infinitude of detailed investi- 

 gations in all parts of the country. 



Ecological phy to geography, which endeavors to find out 

 how and why the different species of plants in various places 

 and under various conditions of life come together in plant- 

 communities. This branch of science, which was founded by 

 Professor E. Warming, must be based upon phytoanatomy 

 and phytophysiology, as the connection between the organi- 

 zation of the vegetable species and their external conditions 

 of life must be investigated. Investigations such as these 

 may yield interesting results in all countries, and are most 

 easily carried on where the conditions of life are uniform 

 over wide areas ; but in a country like Norway, with its varied 

 conditions, they present very great difficulties. 



Historical phyto geography has for its aim the investiga- 

 tion of the changes that in the course of time have taken place 

 in the vegetation of a country — to find out, for instance, when 

 and whence important species have immigrated, how quickly 

 they have spread, why others, that had formerly been more 

 widely distributed, had a more restricted distribution in a 



later period, etc., etc. 



With regard to this last branch of science, the Scandin- 

 avian countries, Denmark, Finland, Norway, and Sweden, 

 present peculiarly favorable conditions ; for there is no doubt 

 that these countries were formerly buried under a continu- 



Ann. Mo. Bot. Gard., Vol. 2, 1915 



(59) 



