UCHORIACEAE. 897 



narrowed ai the base, truncate. Pappus of very copious soft white simple capil- 

 lary bristles, usually falling away connected, sometimes with I or 2 stouter ones 

 which fall separately. [The Greek name of the Sow-thistle.] About 45 species, 

 of the Old World. Besides the following, another occurs on the Pacific Coast. 



Involucre glandular-pubescent ; heads nearly 25 mm. high. I. S. arvcnsis. 



Involucre glabrous; heads 12-16 mm. high. 



Auricles of the leaves acute; achenes striate and transversely wrinkled. 2. S. oleraceus. 



Auricles rounded; achenes ribbed, not transversely wrinkled. 3. S. asper. 



1. Sonchus arvensis L. CORN SOW-THISTLE. MILK THISTLE. (I. F. f. 

 3534-) Perennial by deep roots and creeping rootstocks, glabrous; stem leafy 

 below, paniculately branched and nearly naked above, 6-12 dm. high. Lower and 

 basal leaves runcinate-pinnatifid, spinulose-dentate, narrowed into short petioles, 

 the upper pinnatifid or entire, lanceolate, clasping; heads several or numerous, 

 corymbose-paniculate, 3-5 cm. broad, bright yellow, very showy; bracts as also 

 the peduncles glandular-bristly; achenes oblong, with about 10 rugose longitudinal 

 ribs. In low grounds along salt meadows and streams, N. J. to Que. and at Great 

 Salt Lake, Utah, and in fields and along roadsides, Newf. to Minn. Nat. from 

 Europe. July-Oct. 



2. Sonchus oleraceus L. ANNUAL Sow -THISTLE. HARE'S LETTUCE. (I. F. 

 3535-) Annual, with fibrous roots; stem leafy below, nearly simple, 3-30 dm. 

 high. Basal and lower leaves petioled, lyrate-pinnatifid, 10-25 cm - l n g> tne ter- 

 minal segment commonly large and triangular, the margins denticulate with 

 mucronate or scarcely spiny teeth; upper leaves pinnatifid, clasping by an auricled 

 or sagittate base; uppermost leaves often lanceolate and entire; heads several or 

 numerous, pale yellow, 18-30 mm. broad. In fields and waste places, a common 

 weed in most cultivated parts of N. Am. except the extreme north. Also in Cent, 

 and S. Am. Nat. from Europe. May Nov. 



3. Sonchus asper (L.) All. SPINY or SHARP-FRINGED SOW-THISTLE. (I. F. f. 

 3536.) Annual, similar to the preceding species; leaves undivided, lobed or some- 

 times pinnatifid, spinulose-dentate to spir.ulo^e-denticulate, the lower and basal 

 ones obovate or spatulate, petioled, the upper oblong or lanceolate, clasping by an 

 auricled base; heads several or numerous, 25 mm. broad or less; flowers pale yel- 

 low. In waste places throughout most of our area and in tropical and S. Am. 

 Widely distributed as a weed in nearly all cultivated parts of the earth. Nat. 

 from Europe. May- Nov. 



15. LACTUCA L. (See Appendix.) 



Tall leafy herbs, with small panicled heads of yellow, white or blue flowers, 

 and alternate leaves. Involucre cylindric, its bracts imbricated in several series, 

 the outer shorter, or of I or 2 series of principal nearly equal inner bracts, and 

 several rows of short outer ones. Receptacle flat, naked. Rays truncate and 5- 

 toothed at the summit. Anthers sagittate at the base. Style-branches mostly 

 slender. Achenes oval, oblong or linear, flat, 3-5 -ribbed on each face, narrowed 

 above or contracted into a narrow beak, which is somewhat expanded at the sum- 

 mit into a small disk bearing the copious soft capillary white or brown pappus- 

 bristles. [The ancient Latin name, from lac, milk, referring to the milky juice.] 

 About 95 species, natives of the northern hemisphere. 

 * Pappus bright white. 



I. Leaves spiny-margined and often with spiny or hispid midribs; flowers yellow. 

 Heads 6-12-flowered ; involucre very narrow, 8-12 mm. high i. L. Scariola, 



Heads 12 -20- flowered; involucre broader. 



Involucre 16-18 mm. high; achene about as long as its beak. 2. /,. Ltidoriciana. 

 Involucre 8-12 mm. high; achene longer than its beak. 6. L. sagittifolia. 



2 Leaves neither spiny-margined nor with spiny midribs (rarely spinulose in No. 4). 



(a) Achenes very thin, flat, contracted into filiform or tapering beaks. 

 Outer involucral bracts abruptly shorter than the inner; heads 8-14 mm. high; flowers 



yellow to red (blue in No. 5). 

 Leaves, or some of them, pinnatificf. 



Plant glabrous throughout, 1-3 m. high. 3. /,. Canadensis. 



Leaves, at least their midribs, hirsute. 



Beak of the achene as long as its body; flowers yellow. 4. L. htrsuta. 

 Beak of the achene less than half as long as its body; flowers blue. 



5. Z,. Morssii. 



