104 COMPOSITiE. AsTKR. 



We are greatly indebted to several botanists and public institutions of this coun- 

 try for the use of their entire collections of ^^i merican A sters ; and we would especi- 

 ally render our acknowledgments to fcir Wm. Hooker, who, by most liberally en- 

 trusting to our care his vast materials in this and other allied genera, has aftbrded 

 the most important assistance. Notwithstanding the very favourable opportunities 

 we have enjoyed, our arrangement of this, probably the most difficult genus in 

 North American botany, although the result of much labor, is by no means so satis- 

 factory as could be desired. -A Ithough much remains to be done before our species 

 can be considered as well settled, still we trust that our attempt will be found to have 

 contributed to this result, and that most of our indigenous A sters may be satisfactorily 

 identified by the student. The chief remaining difficulties relate to the species of the 

 sections Dumosi and SaUcifnlii of A ster proper, which may probably be hereafter 

 much better defined, and also somewhat increased in number, in some instances 

 perhaps by the separation of species which we have ventured to unite, as well as by 

 the identification of various cultivated plants with their native originals. It is well 

 known that many of the enumerated species, both of earlier and later authors, 

 have been described from plants long cultivated in European gardens, where they 

 have doubtless undergone great alterations in appearance ; to say nothing of the 

 strong probability of occasional hybridization. A large, and indeed increasing 

 number of these are only known as garden plants ; and it is probable that many 

 will never be identified with their original types; even supposing them to have 

 been derived in all cases from this country, which is by no means certain. As 

 we have chiefly directed our attention to the indigenous plants, and have drawn our 

 descriptions from these alone, we have thought it advisable to bring together, at the 

 close of our account of the proper A sters known to us, those species of garden ori- 

 gin which we have not identified with native specimens. A fuller comparison than 

 we have been able to institute will doubtless considerably reduce their number. 

 Those botanists who are most familiar with our A sters in their native situations, 

 and with the changes produced by difference of soil, exposure, season, &:c. will not 

 be greatly surjDrised at numerous reductions of species which others may think un- 

 wairanted. We have only to say, that we have seldom ventured upon such reduc- 

 tions, except on the authority of a full suite of specimens which appeared to present 

 absolute transitions. A n obvious difference between two or three specimens is 

 often entirely inappreciable in a fuller series, and thus loses its value as a means of 

 distinction : but the claims of a genuine species are generally confirmed by a large 

 number of specimens. It must, however, be admitted that, in this as in all large 

 and natural genera, several species which we cannot but consider as distinct (such 

 for instance as A. cordifolius and A. sagittifolius) do frequently present very puz- 

 zlino" intermediate fonns; and that an apparent transition is not always real. 'Vet 

 it is better, perhaps, to hazard the occasional reduction of even true species to 

 varieties, than to multiply species which we are confessedly unable to define. We 

 may remark, in conclusion, that we are the more inclined to act upon our own con- 

 victions, on account of the very frequent and wide disagreement even of the highest 

 authorities upon this genus. 



§ 1. Involucre ohovate-campanulale ; the scales regularly imbricaled in several 

 series, appressed, nearly destitute of herbaceous tips; the exterior successively 

 shorter: receptacle alveolate : raysQ-\b: appendages of the style subulate- 

 lanceolate, recurved or diverging, minutely hispid : bristles of the pappus 

 unequal, rather rigid; the inner series mostly slightly thickened toicards the 

 apex: achenia linear, slender, scarcely compressed, somewhat ^-angled or 

 striate: stem corymbose at the summit: leaves {ample) mostly petiolcd, 

 coarsely serrate ; the radical and lower cauline on long petioles, cordate. — 



BlOTIA, DC. 



1. A. corymbosus (Ait.): stem slender, often flexyous, terete; leaves 

 membranaceous, coarsely or incisely and unequally serrate wiih sharp 

 spreading teeth, conspicuously acuminaie, all but ilie uppermost cordate and 

 on slender naked petioles, ovate or ovate-lanceolate ; heads loosely corym- 

 bose; involucre shorter than the disk; the exterior scales roundish-ovaie; 

 rays (white) 6-9.— Ait. Kew. (ed. 1) 3. p. 207; Willd. spec. 3. p. 2036; 



