CRUCIFER^ 



53 



FiQ. 42.— 

 Brassioa 

 nigra. 



pod constricted between the seeds, 

 and tipped with a flattened, often 

 1-seeded beak. A troublesome 

 field weed, introduced. 



2. B. nigra, (L.) Koch.. Black 

 Mustard. 

 More slender and not so rough 

 as the preceding; lower leaves 

 with a large terminal lobe ; pods 

 short, erect; seeds black. The 

 mustard of commerce, frequently 

 introduced as a weed. 



8. ARABIS.' Rock Cress. 



Pods linear, long and flat, 

 often appressed, seeds in 1 or j-m. 41. _ Srassica 

 2 rows; stigma 2-lobed; leaves , arvensis. 



pinnatifld if at all divided, the 



root leaves more or less petiolate, often forming a rosette, the stem 

 leaves sessile, often clasping. Usually annual or biennial herbs, 

 glabrous or nearly so, with white, yellowish, pink, or purple flowers. 



* Seeds in one now in the cell. 



t Seeds oblonq or elliptical, small, not winged. 



1. A. lyrata, L. 



Root leaves lyrate-pinnatifid in a rosette ; stem leaves spatulate or linear, 

 base tapering; flowers with white petals but yellowish sepals, the petals 

 much longer than the sepals; pods long, flat, usually ascending. Sandy 

 waste places, Alta. 



2. A. glabra, (L.) Bernh. Towek Mustard. ' 

 Biennial, tall, 1—3 ft., erect, glaucous above, slightly pubescent below, 



stem usually simple; root leaves petioled, oblanceolate to oblong, dentate 

 and hairy; stem leaves sessile, lanceolate with sagittate base, glabrous, entire 

 or the lower sparingly dentate; flowers yellowish white, the petals only 

 slightly longer than the calyx; pods linear, erect, and appressed. A. per- 

 foliAta, Lam.) Waste places and fields, Man.-Alta. 



tt Seeds okbicular and winged. 



3. A. hirsiita, (L.) Scop. 



Stem erect, usually simple, rough, hairy or nearly glabrous; root leaves 

 obovate or spatulate, dentate, on margined petioles; stem leaves lanceolate, 

 dentate, sessile, clasping the stem at the base; flowers white or greenish 

 white; pods linear, appressed. Rooky or sandy banks, Man.-Alta. 



