CLASSIFICATION OF ANGIOSPERMS. 553 



silicic, which varies in shape in the different genera (Fig. 310). 



Brassica alba (white mustard). The plant is a slender, 

 branching, more or less hispid (bristly hairy) annual or biennial 

 herb usually less than 0.5 M. high, with deeply pinnatifid lower 

 leaves and lanceolate, dentate upper leaves. The flowers are 

 yellow, and the silique is densely hispid, constricted between the 

 seeds and terminated by a long, flat, sword-like beak (Fig. 310). 

 The seeds are official as white mustard (Sinapis alba) but are 

 known in commerce as yellow mustard. 



Brassica nigra or black mustard, the seeds of which constitute 

 the official black mustard (Sinapis nigra), is a larger, more branch- 

 ing plant than Brassica alba, being from I to 3 M. high. The 

 silique is erect, more cylindrical and with a slender, filiform beak 

 (Fig. 310). 



Glucosides similar to those which occur in BRASSICA ALBA and 

 BRASSICA NIGRA are also found in other species of BRASSICA, 

 as well as in the following related plants, but the oils produced 

 are not identical: Horseradish (Roripa Armoracia), the oil being 

 similar to volatile oil of mustard; water cress (R. Nasturtium) ; 

 garden radish (Raphanus sativus) ; Sisymbrium Alliaria of Eu- 

 rope, and the hedge mustard (S. officinale) naturalized in the United 

 States; TURNIP (Brassica Rapa) of Europe; field penny-cress 

 (Thlaspi arvense) of Asia and found in waste places in the 

 Eastern and Middle United States ; the narrow leaved pepper- 

 grass (Lepidium ruder ale) naturalized from Europe ; scurvy-grass 

 (Cochlearia officinalis) of Northern and Middle Europe, the herb 

 of which, known as HERBA COCHLEARIA, is used in medicine; 

 " HONESTY" (Lunaria annua) common in cultivation on account 

 of the ornamental use of the dry pods ; Parrya macrocarpa of 

 Southern Europe; treacle mustard (Erysimum cheiranthoides) of 

 Northern Europe and the United States, and garlic mustard (E. 

 Alliaria). 



The seeds of most of the Cruciferae are also rich in fixed oils, 

 and the commercial oils are obtained from the following species : 

 Wild mustard or charlock (Brassica arvensis) naturalized in the 

 United States from Europe ; Hesperis tristis of Southern Europe ; 

 cabbage (Brassica oleracea). An INDIGO- forming glucoside is 

 found in Isatis tinctoria of Europe and /. indigotica of China; 



