7] TYPES AND AREAS OF NATURAL DISTRIBUTIONS 185 



Fig. 46. — Map showing arctic circumpolar distribution as exemplified by Edwards's 

 Eutrema {Eutrema edivardsii). (From data kindly supplied by E. Hulten.) The 

 broken line indicates the southern boundary of the Arctic as proposed by the 

 present author, and the 10 sectors (given Roman numerals I-X) into which 

 the region is divided are those he employs in phytogeographical citations. 



