SAPINDACEZ. SILVA OF NORTH AMERICA. 79 
ACER. 
FLowErs regular, diceciously or moneciously polygamous, rarely perfect, or dic- 
cious; calyx generally 5-parted, the lobes imbricated in estivation; petals usually 5, 
imbricated in estivation, or 0; ovary 2-celled; ovules 2 in each cell, ascending. Fruit 
a double samara. 
Acer, Linnezus, Gen. 112.— Adanson, Fam. Pl. ii. 383. — Negundo, Moench, Meth. 334.— Endlicher, Gen. 1056. — 
A. L. de Jussieu, Gen. 251. — Endlicher, Gen. 1056. — Meisner, Gen. 56.— Gray, Gen. Ill. ii. 201. — Bentham 
Meisner, G'en. 56. — Gray, Gen. Ill. ii. 199. — Bentham ‘ & Hooker, Gen. i. 409. 
& Hooker, Gen. i. 409. — Baillon, Hist. Pl. v. 427. Negundium, Rafinesque, NV. Y. Med. Rep. hex. 2, v. 350. 
Trees or rarely shrubs, with lmpid or sometimes milky juice, terete branches, scaly buds, the inner 
scales often accrescent with the young shoots, and fibrous roots. Leaves opposite, long-petiolate, 
simple, palmately three to seven-lobed, or rarely entire, or pinnately three to five-foliolate, generally des- 
titute of stipules, deciduous. Flowers in fascicles produced from separate lateral buds and appearing 
before the leaves, or in terminal and lateral racemes or panicles appearing with or later than the leaves. 
Bracts minute, usually caducous. Calyx colored, four to twelve, usually five-parted or lobed, decidu- 
ous. Petals as many as the lobes of the calyx, inserted on the margin or base of the disk, equal, 
erect, colored like the calyx, deciduous; or wanting. Disk annular, fleshy, more or less lobed, with a 
free margin, or rarely rudimentary. Stamens four to ten, usually eight, inserted on the summit or inside 
of the disk, hypogynous or perigynous; filaments distinct, filiform, commonly exserted in the sterile, 
shorter and generally abortive in the fertile flower; anthers oblong or linear, attached at the base, 
introrse, two-celled, the cells opening longitudinally. Ovary two-lobed, two-celled, compressed contrary 
to the dissepiment, wing-margined on the back; styles two, inserted between the lobes of the ovary, 
connate below and divided into two linear branches stigmatose on their inner surface; ovules two in 
each cell, collateral, rarely superposed, ascending, attached by their broad bases to the inner angle of 
the cell, anatropous or finally amphitropous; micropyle inferior. Fruit composed of two samaras sepa- 
rable from a small persistent axis, the nut-like carpels compressed laterally, produced on the back into a 
large chartaceous or coriaceous reticulated wing thickened on the lower margin. Seeds solitary by 
abortion or rarely two in each cell, compressed or irregularly three-angled, ascending obliquely, destitute 
of albumen ; testa membranaceous, the inner coat often fleshy.'. Embryo conduplicate ; cotyledons thin, 
foliaceous or coriaceous, irregularly plicate, incumbent, oblique, or accumbent on the elongated descend- 
ing radicle which is turned towards the hilum.’ 
The genus Acer is represented in all the great geographico-botanical divisions of the northern 
hemisphere, but extends south of the equator only to the mountains of Java.° In the eastern and 
1 The seed of Acer usually ripens in the autumn and germinates 2 The genus may be divided into two sections as proposed by 
the following spring. The seed of the two American species with Maximowicz (Bull. Acad. Sci. St. Pétersbourg, xxvi. 437, 450 [Mél. 
precocious flowers, however, ripens at the end of a few weeks after Biol. x. 591, 609). 
the trees flower, and germinates at once. This is a provision, per- AcER. Flowers polygamous or diccious, petalous or apetalous. 
haps, acquired by these species to insure their perpetuation ; they Leaves simple. 
grow in low wet land, often inundated during the winter, and the Negunpo. Flowers diccious, apetalous (in the American spe- 
seed, if it ripened in the autumn, would often lie in water through cies) or furnished with petals. Leaves pinnately or ternately 
the winter and be in danger of losing its vitality ; but it reaches divided. 
the ground after the water has fallen in the swamps and before the 8 Acer appears to have been unrepresented in the Tertiary Arctic 
exposed surface of the ground has become baked by the hot sun of flora, and to have been rare in that of Greenland. (Heer, Fl. Foss. 
summer, that is when it is in just the condition to insure the ger- Arct. vii. Die tert. Fl. v. Groenl. 125, t. 94, f. 1-3.) It was more 
‘nation of ced: abundant in Spitzbergen at the same epoch (Heer, Fl. Foss. Arct. 
