THE 



47 



same species, especially if age is not regarded. The 

 method is, therefore, not submitted as altogether complete 

 in itself, but as supplemental, and, it is hoped, a useful 

 aid to the usual technical descriptions of the species in the 



works on the subject. 



With regard to the variation referred to above, it is 

 chiefly dependent upon the age of the leaf, but partly also 

 upon the season. Leaves early in the season, though of 

 full size, generally lack character, that is certain charac- 

 teristic features are not well developed. Thin-veined leaves, 



rht be expected, show obliteration sooner than their 



mi 



any sort 



seeme 



opposites. 



It was not easy to find a basis upon whi 

 grouping might be founded. The best that 

 ble was by taking the character of the secondaries as a 

 guide. Inasmuch as the primaries are regular almost with- 

 out exception, they would not serve the purpose. I found 

 that if the secondaries be regular, there will be the im- 



pression of regular veining; and that the more 



5 



ar 



Building upon this basis I was enabled to put the included 

 species into three fairly well defined groups. The first, 

 comprising regular veined leaves, embraces S. alba, S. 

 fragilis, S. lucida, S. phylicifolia, and S. argyrocarpa. 

 The second, exhibiting partly irregular veining, consists of 

 those species in which the secondaries, though often quite 

 regular, sometimes lapse into marked irregularity. This 

 group embraces S. nigra, S. amygdaloides, S. adenophylla, 

 S. discolor, S. cordata, S. sericea, S. petiolaris, S. myrtil- 

 loides, andS. Candida. Lastly, the third group comprises 

 those species which have their secondaries almost invariably 

 irregular, resulting in an impression of great and general 

 irregularity of veining. In this group come S. humilis, S. 

 tristis, S. rostrata, S. glaucophylla, S. balsamifera, S. pur- 

 purea, S. Babylonica, S. longifolia, S. herbacea, and S. Uva 

 Ursi. S. viminalis, at the suggestion of the distinguished 

 salicologist, M. S. Bebb, Esq., was left off of the list. 



2 



