j VI. CRUCIFERJE. 43 



and pointed, ^ to 1 inch long. Flowers few, with minute white petals. 

 Pods about a line and a half long, and oblong, or sometimes shorter, 

 and nearly globular, with 5 or 6 seeds in each cell. 



In the shallow edges of alpine ponds and lakes, in northern Europe, 

 Asia, and America, and more rarely in central Europe. Scarce in 

 Britain, in the mountains of Scotland, north-western England, North 

 Wales, and western Ireland. Ft. summer. 



XVII. THLASPI. PENNYCRESS. 



Annuals or low perennials, the leaves usually undivided, the upper 

 ones clasping the stem, the flowers small and white. Petals equal, or 

 nearly so. Pod orbicular or obovate, flattened laterally at right angles 

 to the narrow partition, the valves boat-shaped, their midrib or keel 

 more or less expanded into a green wing surrounding the pod. Seeds 



2 or more in each cell, Radicle accumbent. 



A small genus, spread over Europe, northern and central Asia, and 

 North America, distinguished from Iberis and Lepidium by having more 

 than 1 seed in each cell of the pod, from all others by the winged 

 pod. 



Pod (including the broad wing) orbicular, about 6 lines broad 1. T. arvense. 

 Pod obovate or obcordate, not 3 lines broad. 

 Biennial or perennial. Pod longer than broad, with 6 or 8 seeds 



in each cell 3. T. alpestre. 



Annual. Pod nearly as broad as long, with about 4 seeds in 



each cell 2. T. perfoliatum. 



1. T. arvense, Linn, (fig. 96). Mithridate Mustard. An erect, glab- 

 rous annual, 6 inches to a foot high or rather more, simple or branched 

 in the upper part. Radical leaves stalked, but soon disappearing. Stem- 

 leaves oblong or lanceolate, usually marked with a few coarse teeth ; 

 the lower ones narrowed at the base, the upper clasping the stem with 

 prominent auricles. Pods in a long raceme, about half an inch in 

 diameter, including a very broad wing, deeply notched at the top, with 

 a very minute style in the notch. Seeds usually 6 in each cell. 



In cultivated and waste places, throughout Europeand Russian Asia 

 to N.W. India. Widely scattered over various parts of Britain, but not 

 so common with us as on the Continent. Fl. spring and summer. 



2. T. perfoliatum, Linn. (fig. 97). Per foliate P. A glabrous annual, 

 branching^ the base, or nearly simple, the stem ascending or erect, 



3 to 6 inches high. Radical leaves spreading or tufted, stalked, ovate 

 or orbicular ; upper stem-leaves ovate or oblong, clasping the stem with 

 rather large rounded auricles. Pods not half th"e size of those of T. 

 arvense, with narrower wings, and the notch much broader and more 

 open. Style nearly as long, or longer than the notch. Seeds usually 



4 in each cell. 



In stony pastures and waste places, chiefly in limestone districts, in 

 central and southern Europe, and temperate Asia. In Britain appa- 

 rently confined to a few localities in E. Gloucestershire. Fl. spring. 



3. T. alpestre, Linn. (fig. 98). Alpine P. A. glabrous biennial or 

 perennial, forming a shortly branched or tufted stock, with obovate 

 oval or oblong, stalked, radical leaves. Stems simple, erect or ascend- 

 ing, about 6 inches high j the leaves narrow, clasping the stem with 



