WHITE MUSTARD 383 



the potassium myronate, splitting it into potassium hydrogen 

 sulphate, sugar and allylthiocarbimid or ' mustard oil.' 

 The decomposition may be represented thus : — 



C,<,H.eKNS,0„ = KHSO, + C,H„0. + C3H5NCS. 



Potassium myronate. Potassium hydrogen Sugar. ' Mustard oiL' 



sulpliate. 



' Mustard oil ' has an extremely pungent taste and smell ; it 

 gives off vapour, small quantities of which bring tears to the 

 eyes ; when the oil is applied to the skin, it immediately pro- 

 duces blisters. 



14. White Mustard {Brassica alba N\%. = Sinapis alba L.). 

 — An annual plant grown chiefly as food for sheep in this 

 country, and for ploughing in as a green manure to enrich the 

 ground in humus. Its seeds are also used for the manufacture 

 of oil, and for the preparation of table mustard as in the last 

 species. Young seedlings are used as a salad with cress. 



Some botanists consider white mustard not a true native of 

 the British Isles. 



When grown for seed it does not occasion any trouble as a 

 weed in subsequent crops after the manner of black mustard, as 

 its seeds all germinate at once when conditions are favourable, 

 and the young plants are then readily destroyed. 



Seed and Germination. — The seeds are much larger than 

 those of black mustard and pale yellow. 



The seedling has notched cotyledons, and its first foliage-leaves 

 are pinnatifid or pinnately lobed, as in Fig. 5, thus differing 

 from turnip and black mustard. 



Stem and Leaves. — The stem grows from t to 3 feet high, 

 and is generally branched and covered with rough hairs. 



All the leaves are bright green and rough ; they are lyrate- 

 pinnatifid or pinnate, with irregular lobes. The terminal lobe of 

 the leaf is usually small compared with those of the leaves of 

 turnip and black mustard. 



