20 BULLETIN 179, U. S. DEPARTMENT OF AGRICULTURE. 
10. Young branches glabrous; pubescence of the leaves usually - 
more abundant along the midrib and more or less tufted in the 
axils of the lateral veins. Flowers 9 or 10 mm. broad, the 
calyx lobesiqlandulan's: lor. SSS e ae Cele. SURE R eee 5. ae fd: 
10. Young branches more or less pubescent; pubescence of the 
leaves usually neither more abundant along the midrib than 
elsewhere, nor tufted in the axils of the lateral-veins. Flowers : 
6 to 10 mm. broad, the calyx lobes eglandular............... ive 
11. Leaves lanceolate to ovate-lanceolate, rather strongly condupli- 
cate or trough shaped. Fruit ripening in July and August.. P. reverchonii. 
11. Leaves ovate to oblong-ovate or sometimes slightly obovate, 
usually not trough shaped. Fruit ripening in June.......... P. rwularis. 
12. Leaves usually 6tol10cm.long. Calyx lobes glandular........-- P. munsoniana. 
12. Leaves mostly 2to6cm.long. Calyx lobes eglandular........... 132 
13. Leaves oblong-lanceolate to obovate-lanceolate, mostly 4 to 6 
cm. long. Flowers 10 to 14mm. broad. Fruit ripening at the 
Arnold: ArboretumiinY Septemberic: asa) 2 ee eee P. orthosepala. 
13. Leaves lanceolate, oval-lanceolate, or oblong-oval, 2 to 6 cm. 
long. Flowers 8 to 12 mm. broad. Fruit ripening from the - 
last of May, in the South, to the first of September (subsp. 
WOESONL). oo iow seo ose ce oe ao einen as ae ate ee ee EE P. angustifolia. 
14. Leaves lanceolate to oval-lanceolate or sometimes ovate or oval, 
not strongly reticulate veiny below, and glabrous or pubescent. 
Flowering pedicels glabrous or only sparingly pubescent........ 165. 
14. Leaves ovate, oval, or nearly orbicular, rarely somewhat obo- 
vate, rather strongly reticulate veiny below, and pubescent. 
Flowering pedicels strongly pubescent.......-.-.----.------+-- 16. 
15. Petioles mostly 7 to 12 mm. long. Calyx lobes only slightly 
shorter than the tube. Tree of the northern Alleghenies and 
southern New-Hngland 22222-22228 tis. base eee eee See P. alleghaniensis. 
15. Petioles mostly 5to9mm. long. Calyx lobes mostly shorter than 
the tube. ‘Tree of the Southern States... -.5.../1.2205..2.2: P. umbellata. 
16. Leaves orbicular to oblong-orbicular, obtuse at the apex........ P. gravesit. 
16. Leaves ovate or oval, rarely slightly obovate, usually acute at 
thevapex 232 5. Se tee cape ee ee ee P. maritima. 
17. Leaves oval or lance-oval, rarely ovate or obovate-lanceolate, 
narrowed or rounded toward the base, petioles 5 to 8 mm. 
long. Flowers 9 to 10 mm. broad, pedicels and calyx finely 
pubescent. 2 25 Che Se eS RESTO: SARE Seep P. gracilis. 
17. Leaves ovate to oblong-ovate, usually rounded at the base, 
petioles 10to12mm.long. Flowers 6 to’7 mm. broad, pedicels 
and calyx glabrous or sparingly pubescent..........-.--.-2+-- P. venulosa. 
18. Leaves lanceolate, oblong-lanceolate or oblong-oval, narrowed or 
rounded at the base, the apex acute oracuminate. Flowering 
pedicels without subtending bracts, or when present the bracts 
minute, not foliaceous. Eastern and Rocky Mountain species. P. pennsylvanica. 
18. Leaves oblong-oval, obovate or rarely lanceolate, narrowed or 
even cuneate toward the base, obtuse or rarely acute at the 
apex. lowering pedicels subtended by small foliaceous dentate 
or laciniate bracts. Southwestern and Pacific coast species.... P. emarginata. 
19. Leaves usually narrowly oblanceolate-spatulate and acute.-....- P. pumila. 
19. Leaves oblong-spatulate to oval or somewhat obovate, acute or . 
