378 Tlie New York State College of Forestry 



but two genera, Dipteronia, represented by a single species in 

 China and Acer, with numerous species widely distributed over 

 the northern hemisphere. 



Leaves opposite, deciduous, simple and palmately lobed or pinnate, long- 

 petioled, chiefly estipulate. Flowers regular, polygamous, dioecious, or rarely 

 perfect, borne in lateral fascicles arising from separate flower-buds before 

 the leaA'es or in terminal and lateral racemes or panicles with or after the 

 leaves; calyx chiefly 5-parted, the segments imbricated; petals 5 or none; 

 disk thick, annular, lobed, or sometimes lacking; stamens 4-12 (usually 7-8), 

 hypog^-nous, with filiform filaments and oblong or linear anthers; pistil con- 

 sisting of a 2-lobed, 2-celled, compressed, wing-margined ovary surmounted 

 by 2 styles which are stigmatic on their inner surface; ovules 2 in each cell. 

 Fruit a double samara, the halves usually long-winged and 1-seeded, and 

 joined at the base; wings papery, thickened on the margin; seed compressed 

 ascending, exalbuminous ; cotyledons thin, folded. 



THE MAPLES. Geims ACER L. 



The genus Acer consists of seventy to eighty species of trees and 

 shrubs scattered over the northern hemisphere of the New and the 

 Old AVorld, one species crossing the equator into Sumatra and 

 Java. Some thirteen forms are found in North America, six 

 species (including one variety) occurring within the area of New 

 York State. Some species are important timber trees producing 

 a close-grained, moderately hard Avood which is prized for furni- 

 ture, in turnery and for interior finish. Maple sugar is obtained 

 from the sap of Acer saccharum Marsh. The maples are also used 

 extensively as shade trees. 



For generic characters, see those of the family. 



KEY TO THE SPECIES page 



1. Leaves simple, palmately veined and lobed 2 



1. Leaves pinnately compound A. Negundo 301 



2. Flowers in terminal racemes 5 



2. Flowers in lateral clusters 4 



3. Racemes erect; leaves coarsely serrate, usually 3-lobed at the apex 



A. spicatum 291 



3. Racemes drooping; leaves finely doubly serrate, 3-lobed at the apex 



A. pennsylvanicum 289 

 4. Flowers appearing with the leaves in nearly sessile, umbel-like, pendant 



corymbs 5 



4. Flowers appearing before the leaves in umbel-like fascicles from separate 



buds 6 



5. Leaves dark green above, glabrous beneath at maturity A. saccharum 293 



5. Leaves yellowish green above, usually downy beneath 



A. saccharum, var. nigrum 2[)5 

 6. Petals wanting; sides of terminal lobe of leaf diverging. . . .A. saccharinum 297 

 G. Petals present; sides of terminal lobe of leaf converging A rubrum 299 



