44 CONTRIBUTIONS FBOM THE NATIONAL HERBARIUM. 



Class II. DICOTYLEDONEAE. 



Stera in cross 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; parts of the flower usually in 4'a or 5's; leaves net-veined. This claw haa 

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

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

 in diameter being by additions from the cambium 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; thiee 

 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 Polype talae. 



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 bristles; such flowers are considered under the 



division, "petals present," or under Gamopetalae. 



Flowers unisexual, one or both kinds in catkins or amenta 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. 141b 



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. 



JUGLANDACEAE (p. 135). 



Leaves pimple; 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 parasite 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). 



