iqiq] SCHNEIDER— AMERICAN WILLOWS 335 



closer inspection shows that the leaves as a whole are narrower 

 and the fruits shorter. In this respect it agrees more with S. 

 exigiia, of which it would represent an extremely glabrescent form. 

 Heller made it a species, and Ball evidently took the same 

 view, as shown by his determinations of herbarium specimens 

 before me, but Rydberg (191 7) quotes it as a synonym of his S. 

 linearifolia, which is the same as var. pedicellata of longifolia. So 

 far as I know the range of this peculiar form, it seems to be restricted 

 to southwestern Idaho (region of Boise River), northwestern 

 Wyoming (Yellowstone Park and northern Lincoln County), and 

 adjacent southern Montana (Carbon and Big Horn counties). 

 There is, to my present knowledge, no 5. longifolia in this region, 

 but it is within the range of 5. exigua. I am therefore inclined to 

 follow a suggestion of C. V. Piper, with whom I have discussed 

 this question, and to refer var. tenerrima as a variety to S. exigua. 

 S. exigua var. tenerrima, nov. comb. — S. longifolia var. tener- 

 rima Henderson in Bull. Torr. Bot. Club 27:354. 1900. — S. tener- 

 rima Heller, Cat. N. Am. PI. ed. 2. 4. 1900. — S. fluviatilis var. 

 tenerrima Howell, Fl. N.W. Am. 618. 1902. — S. linearifolia Rydbg., 

 Fl. Colo. 94. 1906, ex parte; Fl. Rocky Mts. 192. 1917 ex parte. — 

 A t^-po praecipue differt foliis angustioribus linearibus etiam 

 maximis vix ultra 4 mm. latis juvenilibus ut rami noveUi parce 

 breviter sericeis cito glabris vel pilis parcis difficile recognoscentibus 

 vestitis utrinque satis viridibus vix nervatis vulgo pl.m. distincte 

 denticulatis dentibus brevibus subglandulosis saepe satis distanti- 

 bus, ovariis subsessilibus glabris, bracteis oblanceolatis tantum 

 versus basim pilosis, fructibus vulgo pedicello distincto glandulam 

 duplo superante instructis conico-rostratis pedicello excluso ad 

 6 mm. longis. 



Specimens examined. — Idaho: Elmore County, shady rocky banks of 

 mountain rills gone dry, July 12, 1895, L. F. Henderson (fr., type; G.) ; Canyon 

 County, Payette River, sandy bottoms, August i, 1897, L. F. Henderson (fr.; 

 G.) ; Falk's Store, open sandy slopes, alt. 660 m., May 24, 1910, /. F. Macbride 

 (no. 98 m., fr. juv.; G., M., St.; "loose clumps"). — Wyoming: Yellowstone 

 Park, Soda Butte Creek, July 14, 1899, in small clumps on the stony river 

 bottom, A. and E. Nelson (no. 5866, fr.; G., St.); Lincoln County, Jackson's 

 Hole, banks of Gros Ventre River, July 14, 1901 , 5. D. Merrill and E. N. Wilcox 

 (no. 996,fr.; G.,M.; "10 ft."). — Montana: Big Horn County, Crow Agency, 



