161 



P. Richardsonii. Professor Nelson has later recognized the fact 

 that Arabis Brebneriana is not an Arabis. He then distributed 

 it as Stenophragma. Professor Nelson is easily excusable for 

 having redescribed Sisymbrium virgatum under another name, for 

 the more common plant known under that name is not Nuttall's 

 plant, but an undescribed closely related species, which is diag- 

 nosed below. The only specimens of the true P. virgata seen by 

 the writer are the following : Rocky Mountains, near the sources 

 of Sweet Water, Nuttall ; Colorado, Hall & Harbour ; Wyoming, 

 Fort Steele, 1897, Aven Nelson jijj ; Laramie, 1899, Aven & 

 Elias Nelson 68 2j^ 



\^ Pilosella stenocarpa Rydb. 



Biennial or perhaps a short-lived perennial ; stern hirsute with 

 branched hairs, usually simple up to the inflorescence ; basal leaves 

 oblanceolate, 2-3 cm. long, sinuate-dentate, short-petioled, hir- 

 sute-stellate ; stem-leaves sagittate, sessile, about 2 cm. long ; 

 sepals oblong, about 2 mm. long; petals spatulate, 3 mm., 

 long; fruiting pedicels 5-10 mm. long, ascending; pod 2.5-4 

 cm. long, glabrous, scarcely i mm. wide; beak about 0.5 mm. 

 long. 



This closely resembles the preceding in habit, but differs in the 

 smaller flowers, narrower pod, and more distinct style. It is 

 usually also more simple. In P. virgata the petals are usually 

 4 mm. long, the pod 2 mm. thick, and the style obsolete. A 

 duplicate of Nuttall's Sisymbrium virgatum is in the Columbia 

 University herbarium and it matches closely Arabis Brebneriana 

 Nelson. The following specimens of P. stenocarpa have been 

 seen: Wood Mountain, Assiniboia, 1895, JoJin Macoun loooy 

 (type, in Columbia University herbarium) ; Pole Creek, Wyoming, 

 1895, Aven Nelson 1334; Tie Siding, Wyo., 1896, Osterhout ; 

 Leucite, Wyo., 1901, Merrill & Wilcox 480; McCoys, Colo., 

 1903, Osterhout 2^63 . 



^ Pilosella glauca (Nutt.) Rydb. 



Sisymbrium glaucum Nutt.; T. & G. Fl. i : 93. 1838. 

 (?) Turrites diffusa Hook. Fl. Bor.-Am. i : 41, 1829. 



* Aven Nelson i2gg and igo2 may also belong here, but the fruit is too little de- 

 veloped for determination. 



