298 COVILLE 



boundary but so near it as to warrant the assumption that they 

 occur on the other side also. Several species reported from 

 Alaska, in local lists, have been omitted, chiefly because the 

 obvious errors of some identifications throw doubt on all. It is 

 probable, however, that Alaska contains species additional to 

 those herein admitted. These are to be expected along the 

 whole eastern boundary of the territory, where least systematic 

 collecting has been done and where the chance of intrusion of 

 species from the interior continental flora is greatest. 



Of the twenty-three Alaskan willows, five are trees, 10 to 30 

 feet high, seven are erect bushes, commonly 2 to 8 feet high, 

 and eleven are prostrate. The species in these groups are as 

 follows : 



Tree Species. 

 ^S". alaxensis S. behbiana 



S. avipli/olia S. nuttallii 



S. sitchensis. 



Bush Species. 

 S. arbusculoidcs S. giauca 



S. bai'clayi S. niphoclada 



S. commutata S. -pulchra 



S. richardsoni. 



Prostrate Species. 

 S. arctica S. myrtillifolia 



S. chamissonis S. ovalifolia 



S.fusccscens S. fhlchuphylla 



S. glacialis S. polaris 



S. lewcarj)a S. reticulata 



S. stolonifcra. 



Salix myi-tiUifolia is a rare species of whose habit there is no 

 precise collector's record. Our specimens indicate that it is 

 normally a prostrate plant but that when growing in sphagnum 

 moss it tends to assume a somewhat upright form, a character 

 observed in Salix fusccsccns when growing in sphagnum bogs 

 to the south of its more typical range on the northern tundra. 

 Those bushy willows which range upward to timber line or 

 northward to the tundra, as for example Salix ftilchra, often 



