1921] SCHNEIDER, NOTES ON AMERICAN WILLOWS, XII. 91 



d. ANALYTICAL KEYS TO THE SPECIES OF AMERICAN WILLOWS 



In the following keys an attempt has been made to facilitate the de- 

 termination of incomplete material, that is, of specimens of one sex or 

 with leaves only. To accomplish this three different keys are necessary 

 one for specimens with staminate flowers, one for specimens with pis- 

 tillate flowers, and one for specimens with mature leaves. Some species, 

 however, do not appear in each of the three keys, as the staminate flow- 

 ers of several species are still unknown, while of two species the pistilate 

 flowers are unknown. In the key for staminate specimens it has not 

 always been possible to find sufficient differences in the flowers of some 

 closely related species to make their determination without leaves pos- 

 sible. The key for the leaf specimens has presented ever greater difficul- 

 ties, as the leaves of Salix are of a comparatively uniform character and 

 within many species are variable in size, serration and pubescence. It 

 must therefore be stated that this key allows in many cases only an ap- 

 proximate determination if the corresponding flowers are not at hand 

 and the determinations arrived at must be used with caution, unless they 

 can be verified by comparison with correctly determined material. 



The number prefixed to the species apply to their sequence in the 

 systematic enumeration of all American species which will appear in the 

 next issue of this Journal together with a complete index which will con- 



ILLOWS 



I. CLAVIS SPECIERUM SECUNDUM SPECIMINA MASCULA 1 



(Specimina feminea, vide p. 97, sterilia, vide p. 107) 



A. Flores glandulis duobus (ventrali et dorsali) instructi (B, vide p. 9^.) 



a. Stamina 3 v. plura (b, vide p. 92) 



Amenta coetanea vel serotina, fere semper pedunculo distincto foliolato instructa, 

 nunquam normaliter in axillis foliorum maturorum in autumno vel mense 

 Februario apparentia. 



*Amenta satis evoluta vix ultra 8-10 mm. crassa, elongato-cylindrica, saepe 

 flexuosa, pleraque ultra 6-plo longiora quam crassa; filamenta saepissime 

 subcurvata non stricta. 



Ramuli floriferi rubro-fusci ad purpurascentes. 



Foliola pedunculorum utrinque concoloria et stomatifera; bracteae plus- 

 minusve lanceolatae et acutiusculae; ramuli fragiles, floriferi satis in- 

 tense fusci vel purpurascentes. 1. S. Humboldtiana 2. S. nigra. 

 Foliola pedunculorum subtus (initio saepe indistincte) pallidiora, esto- 

 matifera (vel in S. Harbisonii stomatibus paucis instructa); bracteae 

 plusminusve latiores obtusioresque; ramuli (S. Harbisonii excepta) 

 tenaces. 



Ramuli fragiles; folia superne stomatibus paucis instructa; bracteae 

 subacutiores. . . # 12. S. Harbisonii. 



Ramuli tenaces, floriferi saepissime satis sordide vel obscure brun- 

 nescentes vel subcinerascentes. 

 Amenta normaliter ultra 4 cm. longa, foliolis pedunculorum satis 

 longiora 10. S. laevigata etll. S.longi pes 



1 Of the following species the male plant is still unknown: S. crijptodoida, S. Drum- 

 mondiana, S. glacialis, S. latiuscida, 8. laurentiana, S. Nelsonii, S. obtusata S. vara- 

 leuca, S. pclhta, S. Schaffneri. 



