18. A. azùreus, Lindl. Stem rather rough, erect, racemose-compound at the summit, the branches slender and rigid; _leaves rough, the lower ovate-lanceolate or oblong, heart-shaped, on long often hairy petioles; the others lanceolate or linear, sessile_, on the branches awl-shaped; involucre inversely conical.--Copses and prairies, western N. Y., and Ohio to Minn., and southwestward. Involucre much as in A. lævis, but smaller and slightly pubescent. 19. A. Shórtii, Hook. Stem slender, spreading, nearly smooth, bearing very numerous heads in racemose panicles; _leaves smooth above, minutely pubescent underneath, lanceolate or ovate-lanceolate, elongated_, tapering gradually to a sharp point, _all but the uppermost more or less heart-shaped at base, and on naked petioles_, none clasping; involucre bell-shaped.--Cliffs and banks, Ohio to Ill., and southward.--A pretty species, 2--4° high; leaves 3--5´ long. 20. A. undulàtus, L. Pale or somewhat hoary with close pubescence; stem spreading, bearing numerous heads in racemose panicles; _leaves ovate or ovate-lanceolate, with wavy or slightly toothed margins, roughish above, downy underneath_, the lowest heart-shaped on margined petioles, the others _abruptly contracted into short broadly winged petioles which are dilated and clasping at the base_, or directly sessile by a heart-shaped base; involucre obovoid, the scales less rigid.--Dry copses; common. [++][++] _Leaves conspicuously serrate; heads small; rays pale blue or nearly white._ 21. A. cordifòlius, L. Stem much branched above, _the spreading or diverging branches bearing very numerous panicled heads_; lower leaves all heart-shaped, on slender and mostly naked ciliate petioles; _scales of the inversely conical involucre all appressed and tipped with very short green points, obtuse or acutish_.--Woodlands; very common.--Heads profuse, but quite small. Varies with the stem and leaves either smooth, roughish, or sometimes hairy, also with the leaves all narrower. Apparent hybrids with n. 35 also occur. 22. A. sagittifòlius, Willd. Stem rigid, erect, with _ascending branches bearing numerous racemose heads_; leaves ovate-lanceolate, pointed; the lower heart-shaped at base, on margined petioles; the upper lanceolate or linear, pointed at both ends; _scales of the oblong involucre linear, tapering into awl-shaped slender and loose tips_.--Dry ground, N. Y. and Penn. to Ky., and northward.--Green, but usually more or less hairy or downy; the heads rather larger than in the last, almost sessile. 23. A. Drummóndii, Lindl. Pale with fine gray pubescence; _leaves cordate to cordate-lanceolate, mostly on margined petioles_, the uppermost lanceolate and sessile; _scales acute or acutish_.--Passing into the last. Open ground, etc., Ill. to Minn. and Kan.