DESCRIPTIVE MANUAL 



157 



Fig. 88-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 tfieir vitality 

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

 necessary to spi^y 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. 



Chemdcal 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 

 y2 in. long, 4-comered, 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. Eixp. Sta., 101. 



