OF ARTS AND SCIENCES. 75 



I have omitted from this enumeration the S. Babylonica, which is 

 occasionally planted for ornament. 



Our list of Willows of North America (exclusive of Mexico, &c.) 

 amounts to fifty-eight species [not counting No. 42, S. repens], or 

 rather to fifty-nine, as two are proposed under S. 3Iyrsinites ; while 

 the Scandinavian species, including almost all the European, probably 

 do not exceed forty-five. These fifty-nine American species, when 

 compared with the European as to their affinities, may be classified 

 into the following five groups : — 



I. Those which are common both to the Old and to the New World. 



a. Perfectly identical, although more variable in America than in 



Europe. 



1. Transplanted from Europe for cultivation : 



S. alba, S.fragilis, S. acutifolia, 



S. viridis, S. purpurea, S. viminalis. 



2. Arctic or Alpine species : 



S. vagans, S. reticulata, S. arhuscula, 



S. myrlilloides, S. kerbacea, S. poJaris. 



b. Having forms very little differing from the European : 



(S. cinerea ?), S. glauca, S. arctica, 



S. Lapponum, S. lanata, S. alpestris. 



II. Those which, very widely distributed in the middle parts of North 

 America, appear so analogous to European species that they (or at 

 least some of their forms) cannot be definitely distinguished from 

 them, and so may be considered as subspecies : 



)S. lucida, analogous to S. pentandra. 

 S. irrorata, " S. daphnoides. 



S. phylicoides, " S. phylicifolia. 



S. cordata, " S. hastaia. 



S. copreoides, " S. Caprea. 



S. phkbophylla, " S. retusa. 



III. Those which differ sufficiently in characters from their European 

 relatives to be considered as distinct species, though belonging to 

 types which in the Old World produce fewer forms : 



S. Fendleriana, related to S. pentandra. 



S. Wrightii, " S. alba. 



S. amygdaloides, " S. amygdalina. 



