IV. COMPARISON WITH NEIGHBOURING 



FLORAL DISTRICTS. 



IN Table 6 1 is given a survey of the plant-geographical distribu- 

 tion of red and brown algae collectively, in certain subarctic 

 and boreal floral districts. These are so arranged that those 

 floras with the largest arctic element stand furthest to the left. The 

 arctic and subarctic percentages decrease while the boreal percentage 

 increases to the right. The boreal-arctic group is practically similar 

 everywhere, which is also natural according to the geographical dis- 

 tribution of the group. The warm-boreal group is not represented 

 in the subarctic floras, and the arctic group is quite infinitesimal 

 in SW. Iceland and Nordland, and is entirely absent from S. Iceland 

 and the Faaroes. In regard to species, the cold-boreal group is ex- 

 tremely poor in East Greenland and Spitzbergen, somewhat richer 

 in West Greenland and considerably richer in E. Iceland. 



By grouping the species, as is done above (cf. Borgesen and 

 Jonsson, 14), the character of the floral districts can be deter- 

 mined according to those groups which are richest in species. Thus, 

 I characterize a group as subarctic when more than half of its 

 species are reckoned to the subarctic group. In a similar manner a 

 district is boreal when more than half of its species belong to the 

 boreal groups (bor. arct., cold-bor., and warm-bor.). 



Similarly, in an arctic district the species belonging to the arctic 

 group must constitute more than half of the number of species be- 

 longing to the district, and, in addition to the subarctic group, only 

 the boreal-arctic w^ill be represented. Of the floral districts men- 

 tioned by Borgesen and Jonsson (14) none are arctic according 



1 With the exception of Iceland the numbers of the species of red and brown 

 alg are taken from Borgesen and Jonsson 1. c. (14, p. 22). In regard to East 

 Greenland the numbers are corrected according to Rosen vinge (64), and to West 

 Greenland two species have been added: Ectocarpus maritimns and Chantransia 

 collopodd. 



