160 CRUCTFER^. AraUs. 



mostly entire : petals white, 2 Hues long : pods (immature) an inch loug by two thirds Hue 

 wide, straight, abruptly tipped with a very short thick style, ascending on slender pedicels 3 

 to 4 lines long ; valves nearly nerveless (3-nerved ace. to Vahl) : seeds in 2 rows; the "coty- 

 ledons incumbent." — Proc. Am. Acad. xxv. 124. SIsijmbrium humifusum, Ya,hl,'F\. Dan. 

 t. 2297 • Lange, Medd. Green, iii. 51. — Ungara Bay, N.Labrador, Turner. (Greenland.) 

 The cotyledons are said to be incumbent, but are reprc^^ented only partially so in the figure. 

 Var. pubescens, Watson, n. var. Lower leaves and base of the stem pubescent. — 

 York Factory, Dell, Macoun. The mature pods of this variety, which appears to differ only 

 in its pubescence from the Greenland form, have the valves distinctly nerved, and the nar- 

 row acute seeds with oblique cotyledons, as represented. 



A.* Nuttallii, Robinson, n. sp.i Biennial or usually perennial with a branching rootstock : 

 stems simple and slender, a span high or less, erect or ascending, glabrous above, more or 

 less hirsute below with rather loug simple and often forked hairs : radical leaves spatulate- 

 oblanceolate, acutish or obtuse, entire, an iflch long or less ; cauline narrowly oblong to 

 elliptical, sessile ; petals 2 to 3 lines loug, white : pods short, 6 to 9 lines long by one third 

 line wide, somewhat attenuate to a rather stout style ; valves slightly convex, 1-nerved and 

 faintly veined : seeds in 1 row, elliptical ; cotyledons accumbent! — A. spathidata,l^\x.tt.m. 

 Torr. & Gray, Fl. i. 81 ; Brew. & Wats."Bot. Calif, i. 32; not DC. — Mountains of W. Mon- 

 tana to N. Utah, N. Nevada, and E. Washington, chiefly on low ground in valleys. 

 -)— -I— Cauline leaves auriculate. 



A. Hookeri, Lange. Stems several from a biennial (or perennial ? ) branching rootstock, 

 slender, ascending, branched, a span high, hirsute below with simple or forked hairs : radical 

 leaves oblauceolate, acute, sinuate-dentate, 2 inches long or less, rather densely hirsute with 

 short forked hairs ; petioles ciliate ; cauline leaves lanceolate to linear with a clasping sagit- 

 tate base, mostly entire : sepals and pedicels hairy ; petals white, 2 lines long : pods 1 to 1 J 

 inches loug by three fourths line broad, somewhat attenuate to a very short thick style, 

 ascending or spreading upon spreading pedicels 3 to 6 lines long; valves 1-nerved; seeds in 

 2 rows, minute, oblong ; cotyledons incumbent though slightly oblique. — Medd. Groen. iii. 

 50. Turritis mollis, Hook. Fl. Bor.-Am. i. 40; Horuem. Fl. Dan. t. 2296. — Shore of the 

 Arctic Sea between 107° and 130° W. longitude, Richardson. (Greenland.) 



A. dentata, Tore. & Gray. Biennial, branching from the base, pubescent throughout with 

 fine mostly stellate pubescence : stems lax, ascending or decumbent, 1 to 2 feet loug : leaves 

 all acutely and irregularly dentate, very rarely the lower lyrate-piunatifid ; the radical petio- 

 late, obovate to oblauceolate : flowers very small and nearly sessile ; petals white, a line 

 long: pods very narrow, nearly straight, widely spreading, 8 to 12 lines long, glabrous, on 

 pedicels an inch long, beaked by a very short thick style ; valves very faintly 1-nerved at 

 base ; seeds oblong, in I row, wingless, minute ; cotyledons oblique. — Fl. i. 80 ; Torr. Fl. 

 N. Y. i. 54, t. 7. Sisi/mbrium dentatum, Torr. in Short, Fl. Kentucky, 3d Suppl. 338. — New 

 York to Michigan and Minnesota, south to the Potomac, Tennessee, and Missouri. 



A. perfoliata, Lam. (Tower Mustard.) Glaucous: stem erect, solitary, simple, usually 

 stout and 2 to 5 feet high, commonly hairy near the base : radical leaves lyrately pinnatifid 

 to spatulate-oblanceolate and toothed, usually more or less hirsute or coarsely stellate-pubes- 

 cent ; cauline glabrous, entire or the lower toothed, lanceolate to oblong, auricled at base, 

 1 to 4 inches loug: petals yellowish white, 2 to 3 lines long: fruiting pedicels 2 to 6 

 lines in length : pods strictly erect, 1^ to 4 inches long by one half to two thirds line wide, 

 beaked with a short stout style or the broad scarcely 2-lobed or cupulate stigma nearly 

 sessile; valves rather rigid, 1-nerved and veined; seeds crowded, irregular, somewhat tur^ 

 gid, nearly marginless ; cotyledons partially incumbent. — Diet. i. 219. Turritis glabra, 

 L. Spec. ii. 666. T. macrocarpa, Nutt. in Torr. & Gray, Fl. i. 78. — From the Lower St. 

 Lawrence through New England (where infrequent) to New Jersey and westward to the 

 Saskatchewan, south in the Eocky Mts. to Colorado and N. Utah ; on the Pacific Slope from 

 Oregon to S. California. (L. Calif., Eu., Asia.) The cotyledons vary from accumbent to 

 incumbent in the same pod. 



§ 2. EuARABis. Seeds in one row, at least when mature, orbicular or broadly 

 elliptical, more or less wing-margined ; cotyledons strictly accumbent. 



1 The name of this species has been altered on account of the older and still valid homonym. 



