AMBROSIACEAE 307 



Ga. and Tenn. — Pennsylvania: Monroe; NorThampT' n ; Bucks; 

 Delaware ; Chester ; Lancaster ; York ; Erie ; ALLhGHENY. 



2. Nabalus albus ( L. ) Hook. Rattlesnake-root. White LET- 

 TUCE. (Man. p. 907 ; L F./. J577.) In woods, Me. and Out. to Man., 

 south to Ga. and Ky. — Pennsylvania : Northampton ; Bucks ; Dela- 

 ware ; Chester ; Lancaster ; York ; Montgomery ; Allegheny. 



3. Nabalus serpentarius(Pursh) Hook. Lion's-EOOT. Gall-of-The- 

 Earth. (Man. p. 907; I. F. /. jj/c?. ) Infields and thickets, Ont. to 

 southern N. Y., Fla., Ala. and Ky. — Pennsylvania: Northampton; 

 Philadelphia ; Lancaster ; Allegheny. 



4. Nabalus trifoliatus Cass. Tall RattlESNAke-rooT. (Man. p. 

 907 ; \.V.f. 3379.) In woods and thickets. Me. to Vt., Pa., Tenn. and 

 Mo. — Pennsylvania : Monroe ; Northampton ; Bucks ; Delaware ; 

 Montgomery ; Franklin ; Huntingdon. 



5. Nabalus racemosus (Michx.) DC. Glaucous White-lETTuce. 

 (Man. p. 908 ; I. F. f. JjS^.) In moist open places, N. B. and Anticosti 

 to the N. \V. Terr., south to southern N. Y., N. J., Mo. and Colo. — Penn- 

 sylvania : Stations reported, but no specimens preserved. 



6. Nabalus crepidineus (Michx.) DC. CorymbEd RaTTlESNAKE- 

 ROOT. (Man. p. 908 ; I. F. f. JjSj.) In fields and thickets, western Pa. 

 and N. Y. to Ky., Minn, and Kans. — PeJinsylz'ania : MERCER. 



Family 4. AMBROSIACEAE Reichenb. Ragweed Family. 



Involucral bracts of the staminate heads united : pistillate involucre but little 

 changed at maturity. i. Ambrosia. 



Involucral bracts of the staminate heads distinct : pistillate involucre becom- 

 ing a bur. 2. Xanthium. 



1. AMBROSIA L. 



Leaf-blades palmately 3-5-lobed or merely toothed : receptacle naked. 



1. A. trifida. 

 Leaf-blades i-2-pinnatifid : receptacle chaffy. 2. A. artemisiaefolia. 



1. Ambrosia trifida L. BiTTER-wEED. Great Ragweed. (Man. 

 p. 910; I. F. f. 3592.) In moist soil, Quebec to Fla., the N. W. Terr., 

 Neb., Colo, and Ark. — Pennsylvania: Northampton; Bucks; Mon- 

 roe ; Philadelphia ; Delaware ; Chester ; Lancaster ; Frank- 

 lin ; Allegheny. 



la. A. trifida integrifolia (Muhl. ) T. & G. (Man. p. 910.) Range of 

 type. — Northampton ; Lancaster ; Huntingdon ; Allegheny. 



2. Ambrosia artemisiaefolia L. Ragweed. Roman Wormwood. 

 Hog-weed. (Man. p. 910; I. F. y". jjpj. ) In dry soil and cultivated 

 fields, N. S. to Fla., B. C. and Mex. Also in W. Indies and S. Am.; 

 introd. into Eu. — Pennsylvania : Monroe ; Northampton ; Bucks ; 

 Philadelphia ; Delaware ; Chester ; Franklin ; Allegheny. 



2. XANTHIUM L. 



A. Plants spine-armed : leaf-blades of a lanceolate type, not cordate. 



I. X. spinosum. 



