SEGREGATES OF RHUS 115 
A recension of the species of ToxICODENDRON is no easy 
task; so far from easy, I find it one of the most difficult I have 
hitherto undertaken. The best treatment of the genus extant, 
as to the early and typical species, is that of Dillenius in 1732. 
Linneus twenty years later, as his custom was, reduced the 
genus to Rhus and confused the species. Philip Miller sixteen 
years after this restored the genus, and also the Dillenian 
species of it, adding excellent descriptions of two or three new 
ones. In these two classic revisions of Tournefort’s Toxico- 
DENDRON, and not at all in Linnæus, lie the means of identify- 
ing all the species early recognized. 
The following represents my present understanding of the 
names and principal syonymy of the known species. 
T. VULGARE, Mill, Dict:(1768); Moench, Meth. 73 (1794.) 
Hedera trifolia Canadensis, Cornut. Canad. 96. Toxicoden- 
dron vulgare latifolium, Dill. Elth. 389 (1732). 
Rhus radicans, Linn. in part. excel. vars. £ ory; Small, FI. 
727 in part. 
This type species of the genus will have to rest, in the future, 
as it did with Tournefort, with Dillenius, with Linneus and 
and with Philip Miller, on Cornut’s Hedera or trifolia Canaden- 
sis, of which the Cornutian description is fair, and the figure 
excellent. According to all the authors down to and including 
Miller, it isa shrub that is often upright and rootless above 
ground, but sometimes fixing itself to rocks, walls and fences, 
though never climbing high on trees; its leaflets ovate, perfect- 
ly entire, glabrous, or very nearly so; always with a large fruit 
and this peculiarly depressed-globose, being distinctly broader, 
even by its least diameter, than high. This last character is 
clearly brought out in Cornut’s plate, though I am to be the 
first to mention this mark; and there is no other species in 
which this fact holds. 
Miller seems to have declined to adopt for this the Linnean 
name radicans. There were two reasons for this course. The 
Linnwan “species” was an aggregate of three or more; and 
Dillenius’ name vulgare had priority in its favor. In Miller’s 
early day they had not learned that the law of priority was a 
dead letter anterior to the year 1753. 
