340 BOTANY OF CROP PLANTS 



the mustards from grain fields. All grasses are resistant to 

 injury from this spray, but the young mustards, and niany 

 other weeds, are quite easily killed by it. This is due to the 

 fact that the spray does not adhere so readily to the smooth 

 grass leaves as to the mustard leaves; moreover, although the 

 tips of grass leaves are injured, the growing tissue at the leaf 

 base may not be touched by the spray, and hence the recovery 

 is rapid: 



Related Species. — It is closely related to the white mustard which is de- 

 scribed hereinafter, and to Chinese or Indian mustard (Brassicajuncea). The 

 latter is adventive from Asia in this country, often a bad weed, and sometimes 

 its leaves are used for "greens." In the Indian mustard, the pods are i to 2 

 inches long, and some of the forms have leaves twice the size of those in the 

 ordinary black or white mustards. The Japanese or pot-herb mustard 

 (Brassica japonica) is introduced into the United States. It has thin, soft 

 leaves which are valued as "greens." 



Uses. — The plant is used mainly for garnishing, also in 

 salads and in the preparation of meat dressings and sauces. 

 Occasionally it is boiled like spinach. Table mustard is the 

 ground seeds of black mustard. The aroma and pungency 

 of mixed mustard (table mustard) does not exist in the seed 

 itself, but is given rise to when the ground seed is mixed with 

 water. This pungent, volatile oil is an allylthiocyanate and 

 is formed by the action of a specific enzyme, myrosin, upon 

 potassium myronate — a glucoside present in the seed. 



BRASSICA ALBA (White Mustard) 



This species has characteristics very similar to those of 

 black mustard. It is distinguished from the latter chiefly by 

 its Hghter colored bristly pods, and its Hghter colored and 

 larger seeds. 



The plant is a native of Europe, Asia and northern Africa. 

 It is used similarly to the black mustard, and in addition is 



