NOMENCLATURE—HISTORICAL 5 
except that in one or two cases—notably that of the plant usually known 
as P. latifolium—the American principle ‘‘once a synonym always а 
synonym’’ has led to the adoption of a specific name of more recent 
origin than that first used when the latter, under Viscum, was preoccu- 
pied, even though it does not appear elsewhere under Phoradendron; 
and in two or three instances—e. g. what is here called P. Engelmanni— 
a new specific name has been preferred even though an existing or lapsed 
varietal name might have been used in a specifie sense. An embarrassing 
difficulty is introduced through Professor Urban’s otherwise unimpeach- 
able publications in the latinization of the customary Greek generic 
name Phoradendron into Phoradendrum, which compels a monographer 
to choose between recombining the names of all of Urban’s species under 
the former or recombining the still larger number of earlier and classic 
names under the emended generic name. I have felt that of the two 
regrettable courses the former is preferable; and customary practice 
retains numerous other generic names with the Greek ending. 
HISTORICAL SUMMARY 
The exclusively American genus Phoradendron was differentiated in 
1847 from its Old World equivalent, Viscum, by Nuttall, its essential 
characters being trimerous flowers in simple spikes, with contiguous 
fruiting sepals, as contrasted with tetramerous solitary or simply cymose 
flowers and distinctly separate sepals in Viscum. Almost simultaneously 
with Nuttall, Engelmann recognized the generic separability of these 
New- and Old-world mistletoes, and segregated the latter under the 
name Spiciviscum. Before his description was printed in 1849, however, 
Nuttall’s paper had appeared, so that Dr. Gray, to whom Engelmann's 
manuseript had been sent, though publishing the name Spiciviscum 
treated it as a synonym of Phoradendron, and only one species has ever 
been seriously named under Engelmann's proposed genus. 
Except for a few which Humboldt, Bonpland and Kunth had placed 
in Loranthus, all of the species now referred to Phoradendron which 
had been published prior to Nuttall’s segregation of the genus had 
been described as species of Viscum, so that, so far as they antedate the 
appearance of de Candolle’s monograph of Loranthaceae in the Prod- 
romus, they were brought into position under Viscum in that work. 
Nuttall himself named a number of these as pertaining to his new genus 
and indicated clearly that this was probably equally true of most if 
not all of the American species of Viscum. Apparently unacquainted 
with the publications of Nuttall and Engelmann, Miers in 1851 sug- 
gested that the South American species of Viscum, with anthers dehis- 
cent by slits, were not eogenerie with the European species, the anthers 
