382 CRUCIFER^ 



seedling resembles that of a turnip plant with somewhat small 

 cotyledons. 



Stem and Leaves. — The stem grows to a height of 2 or 3 

 feet, and is branched and covered with rough hairs. The lower 

 leaves are large and rough, lyrate, and of a light green colour : 

 the upper leaves lanceolate and smooth. 



Inflorescence, Flower, and Fruit. — The inflorescence is a 

 long raceme ; the flowers are small, about ^ to ^ an inch across, 

 have spreading narrow sepals and pale yellow petals, the broad 

 parts of which are slightly notched. 



The fruit, which grows upright, and closely adpressed to the 

 stem, is-a somewhat short smooth silique about J to f of an inch 

 long with a short slender beak (5, Fig. 123); each valve of the 

 silique has a single strong well-marked longitudinal nerve. When 

 ripe the pods and seeds are of dark colour, hence the name 

 Black Mustard. 



The whole plant resembles charlock, but can readily be dis- 

 tinguished from the latter by the length, shape, position and 

 nerves of its siliques. 



Black mustard requires for its growth a deep, rich, fertile soil, 

 on which it is generally sown broadcast, at the end of March 

 or beginning of April. It is hoed and thinned in May and then 

 left until September, when it is cut rather green and allowed to 

 ripen in small carefully made stacks. 



Composition. — The seeds of black mustard contain about 25 

 per cent, of a fixed oil, which is sometimes extracted from the 

 ' dressings ' obtained in the manufacture of table mustard, and 

 used for adulterating or mixing with rape and other oils. The 

 seeds when ground and mixed with water give rise to a some- 

 what volatile product known as ' mustard oil ' ; the latter does 

 not, however, exist ready formed in the seed, but is produced 

 by the action of an enzyme, myrosin, upon a glucoside known 

 as sinigrtn or potassium myronate, both of which are present 

 in the seeds. In the presence of water the myrosin decomposes 



