300 COVILLE 



Four of these species, arbusculotdes, myrttll(folza, nifhoclada^ 

 and rzchardsom, are believed to belong to the Hudsonian flora, 

 and two, hehbiana and nuttallii^ to the next southerly flora, the 

 one known technically as the Canadian. Thus, while there is 

 considerable diversity in the zonal relationship of the species of 

 this group, they may be considered prevailingly Hudsonian, or 

 one stage more southerly than the Siberian species. 



The remaining species, four in number, belong to the Pacific 

 coast flora. They are : 



S. bar clay i S. sitchensis 



S. commutata S. stolonifera. 



Stolonifera is a local alpine species occupying a restricted 

 area in the coast range of mountains from the vicinity of Juneau 

 to Yakutat Bay, and the others are characteristic species of the 

 so-called Sitkan flora, a modified Canadian flora with some 

 Hudsonian elements, all adapted to the conditions of great 

 humidity that prevail along a narrow strip of the Pacific coast 

 from Oregon to southern Alaska. The average zonal position 

 of these species is about the same as that of the preceding group. 



To facilitate the identification of specimens, two keys have 

 been prepared, a shorter one intended for use with typical 

 specimens, and a longer one intended to bring out more pre- 

 cisely the characters of the various species and to cover the 

 normal variations. The specimens cited cover primarily the 

 collections of the Harriman expedition. Secondarily they cover 

 the collections of Alaskan willows in the National Herbarium, 

 and in the herbaria of the Missouri Botanical Garden, the New 

 York Botanical Garden, and Columbia University. The last 

 three collections, through the courtesy of the directors of these 

 institutions, were loaned for use in preparing this paper. 



As a further aid in recognizing species, each is illustrated by 

 drawings made by Mr. F. A. Walpole. The drawings for the 

 plates were made in the field from living plants ; those for the 

 text figures were made from herbarium specimens. 



Key to Alaska Willows, Based on Typical Complete 



Specimens. 

 Ovaries smooth. 



Catkins sessile on old wood S. richardsoni^ p. 315. 



