composite;. 405 



somewhat scabrous: leaves once or twice pinnatifid: fr. mostly solitary 

 in the axils, turgid-obovoid, less than 2 lines long, obtusely short- 

 pointed, rugose-reticulate, either unarmed, or with 4 short blunt or 

 sharp tubercles.— Borders of fields in uncultivated land near the Bay; 

 plentiful on Point IsabeL 



•45. (tJIRTNERA, Medicus. Genus in all respects like AmJirosia, 

 except that the fertile involucre is 1 — 4-fiowered and becomes in fruit a 

 sharply prickly bur. 



1. G. acanthocarpa, Britton, Mem. Torr. Club. v. 332 (1894); Hook. 

 Fl. i. 309 (1833), under Ambrosia. Frauseria Hookeriana, Nutt. (1840). 

 Annual, ditfuse, hirsute or hispid, the stems and branches 1 — 3 ft. long: 

 leaves of ovate or roundish circumscription, 1 — 3 in. broad, bipinnatifid: 

 sterile racemes numerous, short: fruiting involucre with fiat lanceolate- 

 subulate spines.— Sandy soils southward ; but migrating northward 

 along railway embankments. 



2. G. I)ipiniiatifl(la, O. Ktze. Rev. Gen. i. 339 (1891); Nutt. Trans. 

 Am. Phil. Soc. vii. 507 (1841), under Franseria. Perennial, very stout, 

 procumbent, 2-3 ft. long, somewhat hirsute: leaves ovate, 13 in. long, 

 twice or thrice pinnately parted into oblong-linear divisions and small 

 oblong lobes, canescent with a silky pubescence: sterile raceme dense, 

 the heads large: fruit ovate-fusiform, armed with short thick flattish 

 spines, their tips often incurving. — Sandy beaches; very common. June 

 —Dec. 



3. Gr. Chamissonis, O. Ktze. I. c. (1891); Less, in Linnsea, vi. 507 

 (1831), under Franseria. Size, habit, etc., of the last, but leaves cuneate- 

 obovate, or oblong-ovate with cuueate base, obtusely serrate, only some 

 of the lower laciniate-incised: fruiting involucre ovate, the spines broad 

 and channeled. — Habitat of the preceding, but less common. 



46. XANTHIUM, Tournefort. (Cockle-bur.) Coarse annuals, with 

 branching stems, alternate lobed or toothed leaves, and clustered heads 

 of greenish flowers; the staminate clusters uppermost, the pistillate in 

 the leaf-axils. Involucre of staminate heads 1 or 2 series of narrow 

 bracts. Stamens monadelphous but anthers merely connivent. Fertile 

 head a closed ovoid bur-like 2-celled and 2-flowered involucre, 1 — 2- 

 beaked at apex: each flower a single pistil, becoming a thick ovoid 

 achene, the two enclosed in the hardened prickly involucre. 



1. X. sPiNosuM, Linn. Sp. PL ii. 987 (1753). Widely branching from 

 the base, 2 ft. high: leaves ovate-lanceolate, more or less lobed or 



