KEY. 203 



these flowers numerous, in a close head, which is surrounded 

 by a 4-leaved, petaloid, white involucre. A low herb, 3-8 

 inches high. Upper leav-es crowded, apparently whorled. 



Cornus Canadensis, L. 



Flowers without a perianth, of 2 sorts : the central 

 one fertile— that is, an ovary with 3 bifid styles, and the 

 rest, 12 or so, sterile — that is, stamens of unequal length, 

 each jointed to a pedicel, rising from the axil of a little bract; 

 all these naked flowers in a colored, 4- to 5-lobed involucre, 

 which has a gland in each sinus between the lobes. Herbs 

 with a milky juice. Leaves whorled or alternate. 



Euphorbia. 



539. Perianth either none, or merely an obscure 

 margin, bristles, a scale, a cup, etc 540 



An evident perianth present, being either a (com- 

 monly petaloid) conspicuous calyx, or consisting of 2 or 

 several scales, or bracts 564 



540. Grass- or rush-like plants, with terminal (sometimes 

 capitate) spikes, formed of imbricated, 1-flowered scales 

 (glumes). Flower usually of 3 stamens and a 1 -styled ovary, 

 commonly surrounded with bristles (very rarely w^ith scales). 

 Style 2- or 3-cleft. Culms solid. Leaves grass- or rush-like. 

 Sheaths not split. ( Cyperacem^ Sedges) . . ; 551 



Plants not grass- nor rush-like 541 



541. Stem- and scapeless- plants in the form of roundish 

 or oblong, small leaves (frond), ^4 lines in length, grouped 

 or single, floating upon the w^ater, furnished below with 

 loosely pendent roots. Flowers at the margin of the frond, 

 sessile. In place of a perianth, or involucre, an unequally 

 2-lobed spathe. Stamens 2 (sometimes 1) below the ovary. 

 Style simple. Lemna. 



Plants with stems or scapes, striking root into the 



ground, or fixing themselves to stones or pebbles 542 



54^. Maritime, or salt-water plants, submersed 543 



Terrestrial, or fresh-water plants 544 



543. Sessile anthers and pistils arranged alternately in 2 

 rows on the inner side of a flat-linear spadix, enclosed by a 

 spathe. Stems trailing, with tufts of fibrous roots at the 

 joints, and alternate, linear, entire, sheatliing leaves. On 

 sandy banks in the sea. Zostera marina, L. (809). 



