356 Tlie New York titate College of Forestnj 



l-seeded nut, -wiiigcd in some genera; seed small, exalbuminous; cotyledons 

 fleshy. 



KEY TO THE GENERA page 



1. Staminate flowers solitary in the axils of ament-scales; scales of the pistillate 



ament deciduous; nutlet wingless 2 



1. Staminate flowers 3-6 in the axils of ament-scales; scales of the pistillate 



ament persistent, forming a strobile; nutlet winged Betula 3)7 



2. Involucre of the fruit foliaceous, 3-cleft; staminate aments enclosed in buds 



during the winter Carpinus 35fi 



2. Involucre of the fruit saccate, enclosing the nutlet; staminate aments 



exposed during the winter Ostrya 356 



THE HOP-HORNBEAMS. Genus OSTRYA (Michx.) Scop. 



A genus of wide distribution throughout the northern hemi- 

 sphere and including trees with alternate simple leaves, slender 

 terete branchlets, scaly bark, and heavy close-grained wood. 

 Four species have been described, two of which are indigenous 

 to North America. Ostrya virginiana (Mill.) K. Koch., the Hop- 

 hornbeam, is widely distributed in the United States east of the 

 Rocky Mountains. The other species is confined to a restricted 

 area in the southwest. 



Leaves alternate, simple, oblong-lanceolate to oval or obovate, acute or 

 rounded at the apex, rounded at the base, short-petioled^ Flowers monoe- 

 cious, expanding before the leaves; staminate flowers in short-stalked or ses- 

 sile, clustered aments which are preformed the preceding season near the tips 

 of the branchlets, consisting of 3-4 stamens Avith short, bifurcated filaments 

 terminating in hairy anthers, inserted on ;i receptacle at the base of a broadly 

 ovate, acute, concave scale; pistillate flowers in erect, lax aments terminat- 

 ing short leafy branchlets, borne at the base of a narrowly ovate, foliaceous, 

 ciliate scale which persists imtil mid-summer, each flower enclosed in a saccate 

 involucre formed from the union of a bract and two bracteoloes; calyx adnate 

 to the ovary; style short, bearing 2 filiform stigmas. Fruit a small, ovoid, 

 compressed, acute nutlet enclosed in an enlarged, pale straw-colored, saccate 

 involucre, the cluster resemblmg the fruit of the hop, hence the name 

 Hop-hornbeam. 



THE HORNBEAMS. Genus CARPINUS (Touin.) L. 

 Carpinus includes about twelve species of small trees or shrubs 

 scattered over the north temperate zone from Quebec to Central 

 America in the New World and through Europe, Asia, China and 

 Japan in the Old World. They are characterized by smooth gray 

 bark, furrowed and fluted trunks, and a prominently ribbed nutlet 

 subtended by a trilobed, foliaceous, involucral bract. But one 

 species, Carpinus caroliniana Walt, is found in the United States. 



