44 CONTRIBUTIONS FROM THE NATIONAL HERBARIUM. 



Class n. DICOTYLEDONEAE. 



Stens in cro33 section showing a central pith surrounded by a circle or ring of 

 vascular strands, these often merged into a zone of wood; embryo with two cotyle- 

 dons; par+s of the flower usually in 4's or 5*s; leaves net- veined. This class has 

 also been called exogens because there is, especially in the woody plants, a division 

 of the stem into wood and bark vn^h a growing (cambium) layer between, the increase 

 in diameter being by additions from the camljium to the outer part of the wood and 

 to the inner part of the bark. 



Division I. CHORIPETALAE. 



Petals distinct or wanting. The two lower petals are more or less coherent in 

 Fabaceae;the inner pair of petals is united over the stigma in Fumariaceae; three 

 petals are somewhat coherent in Polygalaceae; all the petals are slightly united at 

 base in Oxalis, Ilex, and Malvaceae. The division is also called Archichlamydeae. 

 The group without petals has been called Apetalae; the group with distinct petals 

 has been called Polypetalae. 



A. Petals none, the sepals sometimes colored like petals. In flowers with superior 

 ovary, if only one series of floral envelopes is present, this is assumed to be the 

 calyx. In flowers with inferior ovary the corolla may be present and the calyx 

 wanting or represented by scales or bristle*; such flowers are considered under the 

 division, "petals present," or under Gamopetalae. 

 Flowers unisexual, one or both kinds in catkins or amenti--. Trees or shrubs. 

 Staminate and pistillate flowers in catkins. 

 Ovary many-ovuled. Seeds with copious silky hairs; calyx wanting; stipules 



present SALICACEAE (p . 132) . 



Ovary with 1 ovule in each cell. 



Leaves narrow, acute at base, broadest above the middle; calyx wanting; 



stipules wanting MYRICACEAE (p. 135). 



Leaves ovate to oblong, broadest below the middle; calyx present; stipules 



present .' BETULACEAE (p. 136) . 



Staminate flowers in catkins; pistillate flowers single or clustered (an oblong or 

 spheric head in Moraceae). 

 Pistillate flowers in an oblong or spheric head . Leaves simple . 



MORACEAE (p. 141). 

 Pistillate flowers single or few in a cluster. 

 Leaves pinnate; fruit a large nut inclosed in a dehiscent or indehiscent 

 smooth covering or shuck, the meat or embryo 4-lobed. 



JTJGLANDACEAE (p. 135). 

 Leaves simple; fruit an acorn, or a nut inclosed in a prickly involucre, the 



meat not lobed FAGACEAE (p. 137). 



Flowers not in catkins, perfect or unisexual. 

 Plants woody (trees or shrubs). 

 Leaves opposite. 



Plant a parai^ite on the branches of trees LORANTHACEAE (p. 143). 



Plants not parasitic. 

 Twigs green or red; fruit a pair of asymmetric samaras; leaves simple 



(pinnate in Rulac) ACERACEAE (p. 200) . 



Twigs gray; fruit a single symmetric samara; leaves pinnate. 



Fraxinus (p. 227). 

 Leaves alternate. 

 Flowers (at least the pistillate) in dense globose peduncled heads; leaves 

 about as broad as long, palmately lobed or veined. 

 Leaves deeply 3-7-lobed; branchlets usually corky- winged. 



Liquidambar (p. 173). 



