CRUCIFER^ 25 



dwarf, 1-2 inches, radical leaves spathulate, usually 

 entire ; Tirol, rare ; and C. officinalis, L. {pyrenaica, 

 DC.) ; with cordate more fleshy radical leaves and 

 fleshy stem; abundant on wet mountain-sides. C, 

 Armoi^acia^ L. {Armoracia rusticana, Wett.), Horse- 

 radish, grows in ditches in the lowlands. 



20. PETROCALLIS, Br. 



Petals entire, lilac or pink ; seed - vessel oval, few- 

 seeded ; leaves in a dense rosette, 3-cleft at the apex. 



P. pyrenaicUy R.Br. ; a pretty dwarf alpine plant with 

 pink flowers and wedge-shaped leaves in dense tufts ; 

 common in the Alps, Dauphiny, and Pyrenees. 



21. Erophila, DC. 



Petals bifid, white ; flowers small, on a leafless scape. 

 Not alpine. 



E. vulgaris, DC. {Draba vernay L.), Whitlow Grass; 

 a very small plant, abundant on walls, «&c., in the very 

 early spring. 



22. Draba, L. 



Petals entire, yellow or white ; flowers usually crowded , 

 filaments not toothed; radical leaves entire; seed-vessel 

 many-seeded. 



A. Flowers yellow : — D. aizoides^ L. (PI. 7) ; a beauti- 

 ful alpine plant, with rosettes of rigid linear ciliated leaves 

 and a leafless scape, 1-4 in. high, bearing a short corym- 

 bose raceme of bright yellow flowers; abundant in the 

 Alps, Jura, Pyrenees, and Dauphiny. D. affiniSj Host. ; 

 alpine chain, local ; differs in having the petals four times 



