164 RUTACEAE. 
PTELEA. Hop Tree. 
(Family Rutaceae). 
Shrubs or small trees: decidu- 
ous. Twigs moderate, warty and 
dotted, terete: pith rather large, 
roundish, continuous, white. Buds 
moderate, closely superposea in 
pairs, very low-conical, sessile, 
breaking through the leaf-scars, 
not distinctly scaly, silvery-silky, 
the end-bud lacking. Leaf-scars 
alternate, somewhat raised, rather 
large, horseshoe-shaped when torn 
by the buds: bundle-traces 3: 
stipule-scars lacking. 
Winter-characters:—Ptelea_ tri- 
foliata. Bosemann, 56; Brendel, 
27, 30, pLijae Biteheoek) (1), 4, 
f. 3; Schneider, f. 97. 
To some persons, notwithstand- 
ing its blue-green foliage, Ptelea 
resembles Staphylea when grow- 
ing, but its alternate leaves or 
leaf-scars and very different buds afford a ready and sure 
means of recognition. In winter it is much more likely to 
be mistaken for Phellodendron. 
The importance of twig-characters, obsewsined of which 
need not be restricted to the winter months, is pointed out 
by Greene in the tenth volume of Contributions from the 
United States National Herbarium, where he segregates 59 
nominal western and southwestern species of Ptelea,—in addi- 
tion to an earlier subdivision (Torreya, 5:100) of what is 
here called P. trifolia. 
- Twigs glabrous, buff. (Wafer ash). P. trifoliata. 
Twigs puberulent. P. trifoliata mollis, 
