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 leaves crowded, apparently whorle'd. 



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 640 



An evident perianth jiresent, 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 with scales)! 

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



Sheaths not split. ( Gyperaceoe, Sedges) 551 



Plants not grass- nor rush-like 541 



34:1. Stem- and scapeless-plants in the form of roundish 

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

 or single, floating upon the water, 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. Xiemna. 



Plants with stems or scapes, striking root into the 

 ground, or fixing themselves to stones or pebbles 542 



542, Maritime, or salt-water plants, submersed 543 



TeiTestrial, 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 si 

 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). 



