COMPOUND FLOWERS. 337 



7. LACTUCA (Lettuce). 



1. L. murdlis (Ivy-leaved Lettuce). Florets 5; leaves 

 pinnatifid, variously cut, with the terminal lobe largest ; 

 panicles spreading. Woods and old walls, not uncom- 

 mon. A slender plant, leafy below, 1 2 feet high, 

 with small yellow heads, each of which contains 5 equal 

 florets, and thus resembles" a simple flower of five petals. 

 The panicle has a singularly angular growth ; the fruit 

 is black. Fl. July September. Biennial. 



* There are three other British species of Lactuca, 

 which are less common than the preceding ; L. Scoriola 

 (Prickly Lettuce), which has nearly perpendicular leaves, 

 prickly at the back ; L. virosa (Strong-scented Lettuce) 

 has spreading prickly leaves ; and L. saligna has narrow 

 toothed leaves, and bears its flowers in lateral tufted 

 clusters. The Garden Lettuce (L. sativa) belongs to 

 this genus, but is not a native plant. 



8. SONCHUS (Sow-thistle). 



1. S. olerdceus (Common Sow-thistle, Milk-thistle). 

 Leaves oblong, more or less pinnatifid or entire, 

 toothed, often prickly, the upper ones clasping the 

 stem ; stem branched ; heads somewhat umbellate ; in- 

 volucres smooth. Waste places, and as a weed in gar- 

 dens, common. This plant is commonly known under 

 the name of Milk-thistle, and is much sought after as 

 food for rabbits. FL June September. Annual. 



2. S. arvensis (Corn Sow-thistle, Milk-thistle). 

 Leaves oblong, the lower ones pinnatifid, with the lobes 

 pointing backwards, toothed, heart-shaped at the base ; 

 stem simple ; heads corymbose ; involucre emdjlower-stalks 

 hairy. In similar situations with, the last, from which 

 it may be readily distinguished by its simple stem and 

 much- larger flowers. Fl. August, September. Per- 

 ennial. 



* S. palustris (Marsh Sow-thistle) is a much taller 

 species than either of the preceding, growing 6 8 feet 



2 



