iQiq] SCHNEIDER— AMERICAN WILLOWS 329 



Rydbg., Fl. Rocky Mts. 188. 191 7. —The type of this species was 

 collected by NiiUall with his fluvia lilts, probably ''on the banks 

 of the Lewis River of the Shoshonee" (Snake River in Idaho), 

 because at the type locality of S. fluviatilis on the Columbia in the 

 vicinity of Portland, Oregon, this species is apparently the only one 

 of the LoNGiFOLiAE according to Ball (Box. Gaz. 60:45, in note, 

 1915). Nnltall says: ''This species is also a native of the terri- 

 tory of Oregon, and grew with the preceding, which it strongly 

 resembles" (5. fluvialilis); he does not indicate the exact locaHty. 

 I have a photograph of a so-called cotype of 5. exigua from Herb. P. 

 consisting of a sterile branchlet. The label originally bore the 

 inscription "5. longifolia, Missouri and Arkansas." The name 

 longifolia has been crossed out, and in a similar handwriting is 

 written ''exigua Nutt." Judging by the serration and nervation 

 of the leaves there can be no doubt that the specimen belongs to 

 S. longifolia. I do not know of a true type specimen of S. exigua, 

 but there can hardly be any doubt as to the form Nuttall had in 

 mind. From his phrase "capsulis lanceolatis sessihbus, demum 

 nudiusculis" I infer that the t>^ical S. exigua is a form with, at 

 least in the beginning, hairy ovaries, but Rowlee and other authors 

 ascribe to it glabrous capsules. Ball (1909) is right in stating that 

 it is "variable in fohage characters and sometunes very difficult to 

 distinguish" from S. longifolia. In spite of havmg seen an abun- 

 dant and well collected material, I am still at a loss how to define 

 certain forms and to draw a sharp line between S. exigua on the one 

 hand and such species as 6*. longifolia, S. argophylla, S. Parishiana, 

 and also 5. taxifolia typica on the other. From S. longifolia and its 

 forms it differs chiefly in the opaque color of the canescent leaf- 

 surfaces, bearing a more or less dense appressed tomentum of short 

 silky hairs (especially on the young leaves) of a silvery hue. The 

 leaves are usually smoother with a hardly visible nervation, but in 

 old leaves (for instance in those of the southern form) the veins are 

 sometimes rather well marked ; their margin is mostly entire, but a 

 dentation similar to that of S. longifolia may be observed in the 

 southern forms. The fruiting aments usually are denser and the 

 capsules as a whole shorter. S. argophylla chiefly differs, as pre- 

 viously stated, by its more villous tomentiun, while S. Parishiana, 



