FLORA OF THE DISTRICT OF COLUMBIA. 219 



15. HYDROCOTYLE L. Marsh pennywort. 

 Leaves peltate (the petiole attached at the middle of the blade, not at the base). 



t i ix x 1. H. americana. 



Leaves not peltate. 



Flowers pediceled 2 . H. ranunculoides. 



Flowers sessile 3> H . rotundifolia. 



1. Hydrocotyle americana L. 



In pools and along streams; frequent. July-Aug. Eastern N. Amer. 



2. Hydrocotyle ranunculoides L. f. 



Edges of streams and pools; frequent. May-July. Widely distributed in N. and 

 S.Amer.; also in the Old World. 



3. Hydrocotyle rotundifolia Roxb. 



Well established in the Smithsonian grounds. Summer. Native of ABia. 



16. ERIGENIA Nutt. 



1. Erigenia bulbosa (Michx.) Nutt. Harbinger of spring. 



Along the upper Potomac, chiefly on the islands; rare. Apr. Eastern U. S. 



17. CONTOM L. 

 1. Conium maculahim L. Poison hemlock. 



Collected several times about Washington; doubtfully established. June-July. 

 Native of Eur.; widely naturalized in N. Amer. 



The roots are very poisonous. 



18. SIUM L. 



1. Slum laeve Walt. Hemlock water parsnip 



About pools, Great Falls and Eastern Branch; rare. Sept. Widely distributed in 

 N. Amer. (S. cicutaefolium Gmel.) 



19. PTILIMNIUM Raf. 



1. Ptilimnium capiUaceum (Michx.) Raf. Mock bishop-weed. 



Wet soil, Custis Spring ( Ward) ; not collected recently. Eastern XL S. (Discopleura 

 capillacea DC.) 



20. CICUTA L. 



Leaflets lanceolate or lance-oblong; bulblets none 1. C, macnlata. 



Leaflets linear; bulblets present in the axils of the leaves 2. C. bulbifera. 



1. Cicuta macnlata L. Water hemlock. 



Swamps and low ground; common. June-Aug. Eastern N. Amer. 

 The roots are very poisonous. 



2. Cicuta bulbifera L. 



Reported by Ward from the "Alexandria Canal, opposite the Arlington estate, "and 

 by Holm from Great Falls. Northern N. Amer., south to Va. 



116. COKNACEAE. Dogwood Family. 



Flowers of two kinds, pistillate and staminate, greenish, the parts in 5's, the petals 

 minute or none; leaves alternate; trees 1. NYSSA. 



Flowers all perfect, the parts in 4's, the petals white and showy, or the flowers in 

 heads surrounded by large white petal-like bracts; leaves opposite, except in one 

 shrubby species; trees or shrubs 2. CORNTJS. 



