628 AMBROSIACEAE 
SNAKE Root. A dwarf species, 4 to 1 ft. high, the leaves halberd-shaped, 
upper ones lance-shaped. Summits of Adirondacks and White Mountains. 
July-Aug. 
8. P. racemosa, Michx. (Fig. 7, pl. 167.) Wuuire Lerruce. Smooth, 
stem often with a whitish bloom, 2 to 6 ft. high. Leaves lance-shaped 
to oval or egg-shaped, with low teeth at margins. Flower heads in a dense 
spike, mostly erect, 1- to 16-flowered. Moist soil, Maine and southward 
to New York and New Jersey. Aug.-Sept. 
9.. P. crepidinea, Michx. CorymMBep RATTLESNAKE Root. Stem 
smooth, 5 to 9 ft. high. . Leaves halberd-shaped. Flower heads numerous, 
the involucre hairy, each head containing 20 to 25 flowers. Fields, woods, 
Penna. and New York, Aug.-Oct. 
Famity IV.—AMBROSIACEAE. Racweep FAMILY 
Herbs, mostly weeds, with alternate leaves or the lower leaves 
sometimes opposite. Flowers in small heads of greenish or white 
flowers subtended by an involucre of a few bracts; usually the 
staminate and pistillate flowers are in different heads on the same 
plant or in the same head—but often the two kinds are on differs 
ent plants. The aigrette or pappus representing the calyx is absent 
or reduced to a little rim at the summit of the fruit. The stam- 
inate flowers have a narrow tubular corolla which is small and 
membraneous. The anthers are free from each other or only 
slightly coherent. 
Staminate and pistillate flowers in the same heads. . . Iva 
Staminate and pistillate flowers in separate heads, the heads 
with stamens mostly above. 
Involucre of the pistillate heads bur-like. . . Xanthium 
Inyolucre not bur-like . . . . . . » & Aiea 
Took WAS LL. 
Large coarse herbs, with fleshy leaves, opposite or alternate, and with 
small heads of greenish flowers arranged in spikes, in the axils or soli- 
tary. ‘There are within the head, about half a dozen or less pistillate 
flowers which occupy the outer circle, while within are several flowers with 
both pistils and stamens. Involucre of a few rounded bracts. Receptacle 
small, chaffy. Aigrette none. 
I. ovaria, Bartlett. (Fig. 3, pl. 168.) Marsm Exper. (J. frutescens, 
Man.) A coarse plant, apparently shrubby, with stems from 3 to 12 ft. 
high, growing in salt marshes. Leaves somewhat fleshy, oval to lance- 
shaped, the lower with coarse teeth. Heads in the upper axils. Recep- 
tacle small, with chaff among the flowers. Sea-side, Mass., New York and 
southward, July-Sept. 
2. AMBROSIA, L. 
Coarse weeds, branching, with alternate or opposite leaves, which are 
