DESCRIPTIVE MANUAL 



157 



Fig. 



3-A. Distribution of Wild Mustard. 



previous season. Having sown the small grain on a clean field there 

 is always a chance that some of the seeds will retain their vitality 

 in the soil. If much of this mustard should come up it may become 

 necessary to spray it with iron sulphate. Where the mustard is 

 abundant this is a very effective means of destroying the weeds, 

 using the sulphate at the rate of 100 pounds to a barrel of water. 



Chemical Composition. — According to the University of Minne- 

 sota the chemical composition is as follows :* 



Black Mustard (Brassica nigra Koch.). 



Description. — A tall, coarse, much-branched annual, 2-5 ft. high ; 

 leaves variously divided or only deeply cut, the terminal lobe the 

 largest, sharply toothed, upper leaves small, simple, as a rule linear ; 

 leaves as a rule not smooth, but somewhat bristly, at least on the 

 veins ; flowers yellow, smaller than in charlock ; pods smooth, about 

 y% in. long, 4-cornered, tipped with a slender beak; seeds black or 

 reddish brown, smaller than in charlock; cotyledons incumbent; 

 trichomes not stellate, simple, rough. 



•Snyder: Bull. Minn. Agr. Exp. Sta., 101. 



