466 URTICACEJE. (NETTLE FAMILY.) 



1. P. pumila, Gray. (RICHWEED. CLEARWEED.) Low (3-18' high); 

 stems smooth and shining, pellucid ; leaves ovate, coarsely toothed, pointed, 

 3-ribbed and veiny ; flower-clusters much shorter than the petioles ; sepals of 

 the fertile flowers lanceolate, scarcely unequal. Cool and moist shaded 

 places. July - Sept. 



11. BCEHMERIA, Jacq. FALSE NETTLE. 



Flowers monoecious or dioecious, clustered ; the sterile much as in Urtica ; 

 the fertile with a tubular or urn-shaped entire or 2 - 4-toothed calyx enclosing 

 the ovary. Style elongated awl-shaped, stigmatic and papillose down one 

 side. Achene elliptical, closely invested by the dry and persistent compressed 

 calyx. No stings. (Named after G. R. Boehmer, Professor at Wittenberg 

 in the last century.) 



1. B. cylindrica, Willd. Perennial, smoothish or pubescent and more 

 or less scabrous ; stem (1 - 3 high) simple ; leaves chiefly opposite (rarely all 

 alternate), ovate to ovate- or oblong-lanceolate, pointed, serrate, 3-nerved ; stip- 

 ules distinct ; petioles short or elongated ; flowers dioecious, or the two kinds 

 intermixed, the small clusters densely aggregated in simple and elongated 

 axillary spikes, the sterile interrupted, the fertile often continuous, frequently 

 leaf-bearing at the apex. Moist or shady ground, common. Very variable. 



12. P ABIE TAR I A, Tourn. PELLITORV. 



Flowers monoeciously polygamous ; the staminate, pistillate, and perfect in- 

 termixed in the same involucrate-bracted cymose axillary clusters ; the sterile 

 much as in the last; the fertile with a tubular or bell-shaped 4-lobed and 

 nerved calyx, enclosing the ovary and the ovoid achene. Style slender or 

 none ; stigma pencil-tufted. Homely, diffuse or tufted herbs, not stinging, 

 with alternate entire 3-ribbed leaves, and no stipules. (The ancient Latin 

 name, because growing on old walls.) 



1. P. Pennsylvnica, Muhl. Low, annual, simple or sparingly 

 branched, minutely downy; leaves oblong-lanceolate, thin, veiny, roughish 

 with opaque dots ; flowers shorter than the involucre ; stigma sessile. Shaded 

 rocky banks, E. Mass, and Vt. to Minn., and southward. June - Aug. 



ORDER 100. PLATANACE^. (PLANE-TREE FAMILY.) 



Trees, with watery Juice, alternate palmately-lobed leaves, sheathing stip- 

 ules, and monoecious flowers in separate and naked spherical heads, des- 

 titute of calyx or corolla ; the fruit merely club-shaped 1 -seeded nutlets, 

 furnished with a ring of bristly hairs about the base ; consists only of the 

 following genus (of uncertain relationship). 



1. PL AT ANUS, L. SYCAMORE. BUTTONWOOD. 



Sterile flowers of numerous stamens, with club-shaped little scales inter- 

 mixed ; filaments very short. Fertile flowers in separate catkins, consisting 

 of inversely pyramidal ovaries mixed with little scales. Style rather lateral, 

 awl-shaped or thread-like, simple. Nutlets coriaceous, small, tawny-hairy be- 

 low, containing a single orthotropous pendulous seed. Embryo in the axis of 



