124 PROCEEDINGS OP THE AIMERICAN ACADEMY 



XI. 



CONTRIBUTIONS TO AMERICAN BOTANY. 

 By SiiKKXo Watson. 



Presented April 8, 1891. 



1. Descriptions of some nevj North American Species, chiefly 

 of the United States, with a Revision of the American Species 

 of the Genus Erythronium. 



Arabis Macounii. Biennial, branched from the base, slender, pu- 

 bescent below with mostly stellate spreading hairs, glabrous above or 

 but sparingly puberulent, a foot high : leaves small and narrow, -A inch 

 long or less, the lower very rarely fevv-toolhed, the cauline sagittate 

 at base : flowers very small, pale rose-color, 2 lines long: pods very 

 narrow, 1 to \^ inches long and about -j line broad, glabrous, slightly 

 curved, mostly divaricate on very slender pedicels 2 to 4 lines lung, 

 acute, the stigma nearlj'^ sessile: seeds (immature) appi-oximately 

 1-rowed, apparently wingless. — At Revelstoke, British Colinnbia; 

 collected by Prof. John Macoun, May, 1890. Near A. hirsiita. 



Erysimum arenicola. Caudex much branched and densely tufted, 

 the branches slender; flowering stems about 6 inches high: leaves 

 narrowly oblanceolate, sparingly toothed, acute or acutish, attenuate 

 to a slender base, about an inch long, sparsely appressed-pubescent : 

 pedicels slender, spreading and 2 or 3 lines long in fruit : calyx 4 

 lines long: pods ascending, slender, 1^ to 2 inches long and less than 

 a line broad, compressed and thin-valved, usually attenuate above to 

 a slender style tipped by the depressed lobed stigma : seeds narrowly 

 oblong, a line long; the cotyledons very obliquely incumbent. — In 

 volcanic sand on the Olympic Mountains, Wasliingt'Mi, at 5.000 feet 

 altitude; collected by Mr. C. V. Piper, Septoinber, 1S<>0 (n. 91()). 



SiLENE Macounii. Stems very slender, from a slender branching 

 rootstock, a foot high, minutely puberulent, glandular above: leaves 

 linear-oblanceolate, 3 inches long or less : flowers few, on pedicels ^ 

 to 1 inch long; calyx inflated, oblong-campanulate, 4 or ;"> lines long, 

 with short obtuse teeth ; petals little ex.^erted (G lines long), with a 

 broadly auricled glabrous claw and large thin quadrate and nearly 



