43 



height, in which birds have their nesting places, and, by eating and 

 excreting the seeds, help to spread this pernicious weed. 



Description. — The rather stiff, dark-green, branching stem of black 

 mustard is from 4 to 6 feet in height. The lower part of the stems 

 and branches is more or less bristly hairy, but the upper part is 

 usually smooth. 



The leaves are dark green, somewhat rough, with bristly hairs, and 

 are all borne on stalks. The lower leaves are lobed, the terminal lobe 

 being the largest and the two 

 or more lateral ones smaller. 

 The leaves toward the top of 

 the plant become lance shaped 

 and are slightly toothed. 



The flowers of black mus- 

 tard appear from June to Sep- 

 tember, and are of a bright 

 yellow color. They are rather 

 small, scarcely a quarter of an 

 inch in diameter, the four pet- 

 als spreading and each consist- 

 ing* of a rounded blade with a 

 narrow claw. The petals alter- 

 nate with the pale-green sepals 

 or calyx lobes. The flowers 

 appear in clusters at the ends 

 of the elongating stems, fol- 

 lowed from July to November 

 by the numerous erect pods 

 crowded against the stem in 

 dense narrow clusters. The 

 pods are about 1 inch in length, 

 quadrangular, smooth, and 

 tippedat the apex by the short, 

 persistent style. The seeds 

 contained in the pods are very 

 numerous, small, about one twenty-fifth of an inch in diameter, globu- 

 lar, blackish brown, and finely pitted. 



The plant is an annual, and if care is taken to prevent the distribu- 

 tion of the seeds it is not difficult to exterminate. The seeds possess 

 great vitality, and may remain in the ground for years before 

 germinating. 



Collection of seeds. — The tops may be pulled when most of the pods 

 are nearly mature, but before they are ready to spring open. They 

 should then be placed on a clean, dry floor or shelf, allowing the pods 



188 



Fig. 30.— Black mustard (Brassica nigra (L.) Koch). 



