82 PROCEEDINGS OP THE AMERICAN ACADEMY 



VI. 



A REVISION OF THE NORTH AMERICAN CHENO- 



PODIACE^. 



By Sereno Watson. 

 Bead, AprU 14, 1874. 



The classification of the Chenopodiacece given by Moquin-Tandon 

 in De Candolle's " Prodromus " twenty -five years ago has been ever 

 since substantially accepted and followed, although several of his genera 

 have not been sustained. In the present study of the North American 

 genera, it has seemed best to deviate in some measure from his arrange- 

 ment, partly to make the sequence more natural, in part because the 

 distinctions upon which his divisions are founded do not hold good in 

 the cases under consideration. 



The great variations that occur in the floral envelopes in this order 

 are worthy, from their bearing upon physiological questions, of a more 

 careful study than has been given to them. Stamiuate flowers, where- 

 ever they occur, excepting a single genus, are accompanied by the 

 normal calyx, regularly 4-5-cleft or -parted, and never in any way con- 

 spicuously appendaged. In perfect flowers, likewise, a calyx is always 

 present, but with the number of the sepals not unfrequently reduced, 

 very rarely bracteate or obscurely bracteolate, remaining unchanged 

 in fruit or slightly enlarged, or the lobes becoming thickened or costate, 

 or developing a thin horizontal wing. When the flowers become ex- 

 ceptionally pistillate, the calyx remains the same in character ; but in 

 the proper monoecious and dioecious genera the flowers are decidedly 

 dimorphous, the pistillate being for the most part wholly without calyx 

 and enclosed within bracts. These bracts assume very diverse forms and 

 peculiarities, though their foliaceous character is generally evident, at 

 least in the flower. The wings, when present, corresponding to the 

 margins of the compressed bracts, are always vertical, as are also the 

 dorsal crests. In Grayia and Eurotia (and Ceratocarpus), in which 

 the bracts are obcompressed, the winged marginal nerve in Grayia 



