48 CRUCfFER^E 



with a flat, two-edged, sword-like beak. — Waste ground. — Fl. June, 

 July. Annual. Seedlings of this species are largely eaten, with 

 those of Cress (Lepidium sativum), as salad. 



14. Diplotaxis (Rocket) has spreading sepals ; but differs from 

 the mustards in its flattened pods with membranous valves and 

 seeds in two rows. (Name from the Greek diplos, double, taxis, 

 rank or row.) 



1. D. tenuifblia (Wall Rocket). — Slender, branched, 1 — 2 feet 

 high ; stem woody below ; leaves deeply divided into long narrow 

 segments, glaucous ; flowers f in. across, light yellow, fragrant ; 

 pods short, linear, erect, on very long slender stalks. — On old 

 walls. — Fl. June — September. Perennial. 



2. D. murdlis (Sand Rocket), a less branched, hispid, herba- 

 ceous, and generally annual species, grows in waste ground, 

 especially near the sea. 



*i5. Alyssum, a genus of small plants, mostly hoary with 

 adpressed hairs, with simple leaves, small white or yellow floivers, 

 and rounded, few-seeded pods, includes three alien species, 

 sometimes naturalised : A. incdnum, A. alyssoides, with stellate 

 hairs ; yellow flowers, and persistent sepals ; and A. maritimum, 

 with bi-partite hairs ; white, sweet-scented flowers, and deciduous 

 sepals. 



16. DrAba (Whitlow-grass). — Small herbs, mostly perennial 

 and hoary with stellate hairs ; leaves small, simple, the radical 

 ones in a rosette ; flowers small, white or yellow ; pods compressed 

 or turgid. (Name from the Greek drabe, acrid.) 



* Flowers white 



1. D. murdlis (Speedwell-leaved Whitlow-grass). — Stem leafy, 

 branched, about a foot high ; leaves rough, with stellate hairs, 

 egg-shaped, blunt, toothed, embracing the stem ; pedicels spreading 

 horizontally. — Limestone hills in the west of England ; rare. — 

 Fl. April, May. Annual. 



2. D. incdna (Twisted Whitlow-grass). — Stem leafy, branched, 

 4 — 14 in. high; leaves hoary with stellate down, lanceolate, 

 toothed ; pods twisted. — Mountains, and sandhills near the sea; 

 uncommon. — Fl. June, July. Perennial. 



3. D. rupestris (Rock Whitlow-grass). — Stems several, 1 — 2 in. 

 high, almost leafless ; leaves rosulate, stellately pubescent, ciliate. 

 — In crevices of the rocks and among moss on the summits 

 of some Highland mountains; very rare. — Fl. July, August. 

 Perennial. 



