428 Trans. Acad. Sci. of St. Louis. 
in determining the hybrids. 
The distinction between the par- 
ents may be readily seen from the following comparison : — 
S. amygdaloides. 
Tree stem usually single, limbs 
straight. 
*Bark smooth or only rough, bases 
of branchlets brittle. 
The terminal ends of branchlets 
frequently winter-killed. 
Leaves not usually affected with 
blister-like mite-galls. 
*Under surface of leaves glaucous 
or pale, bluish-green. 
Bases of leaves acute, round, or 
sub-cordate. 
Leaves ovate-lanceolate. 
Veining coarser, stronger, whiter; 
secondaries more regular and 
pronounced 
ite shoots of sterile plant, 
ostly fragrant in early season. 
*Petioles long. 
Stipular in 76 %, deciduous. 
*Stipules all obtuse or rounded. 
*Stipules glandular. 
Petiole at base of leaf often gland- 
. 
*Young shoots and leaves smooth. 
Date of blossoming mostly from 
April 15th to 25th. 
Stamens mostly more than six. 
Scales of pony aments ovate or 
oblong, a 
*Fertile aments loose. 
*Pedicels long. 
S. nigra. 
Stems mostly clustered, more 
crooked limbs. 
*Bark flaky or shaggy, bases of 
branchlets very brittle 
The same not winter killed. 
Leaves frequently affected with 
such galls 
*Green throughout. 
A snisciees obtuseness or even 
truncaten 
Leaves oblong or linear lanceolate. 
Veining very minute, with fre- 
quently a marginal line. 
Young shoots never fragrant. 
*Petioles short. 
Stipular, 57 %, rather persistent. 
*Stipules pointed, all but one. 
*Stipules not glandular. 
The same never glandular. 
Young shoots and mid-rib mostly 
pubescent, 87 %. 
The same after May 3d. 
Stamens mostly less than six. 
Scales shorter, obtuse, more 
villous. 
*The same compact. 
*Pedicels short. 
It is seen that the differences are many, and some of them 
very marked. Those marked with an asterisk indicate the 
