ARACEAE. 



VOL. I. 



Family 13. 



i. Acorus Calamus L. Sweet Flag. Calamus 

 or Flag-root. Fig. 1119. 



Acorus Calamus L. Sp. PI. 324. 1753. 



Leaves linear, erect, 2-6 tall and i' wide or less, 

 sharp-pointed and sharp-edged, with a rigid mid- 

 vein running their whole length, 2-ranked, closely 

 sheathing each other and the scape below. Spathe 

 a leaf-like extension of the scape projecting 8'~3o' 

 beyond the spadix ; spadix spike-like, 2'-$' long, 

 about in diameter, compactly covered with minute 

 greenish-yellow flowers. 



In swamps and along streams, Nova Scotia to Ontario 

 and Minnesota, south to Louisiana and Kansas. Also in 

 Europe and Asia. In our territory fruit is rarely, if 

 ever, formed. The hard ovary is usually found to be 

 imperfect, with 2 or 3 abortive cells and ovules. The 

 plant is propagated by its large rootstocks, which furnish 

 the drug Calamus. Interior of stalk sweet. Myrtle- 

 flag, -sedge or -grass. Sweet-myrtle. Sedge-grass, -cane, 

 -root or -rush. Sea-sedge. Beewort. May-July. 



1827. 



LEMNACEAE Dumort. Fl. Belg. 147. 



DUCKWEED FAMILY. 



Minute perennial floating aquatic plants, without leaves or with only very 

 rudimentary ones. The plant body consists of a disc-shaped, elongated or irreg- 

 ular thallus, which is loosely cellular, densely chlorophyllous and sometimes bears 

 one or more rootlets. The vegetative growth is by lateral branching, the branches 

 being but slightly connected by slender stalks and soon separating. In the autumn 

 these disconnected branches fall to the bottom of the ditch or pond, but rise and 

 again increase in size in the spring. The inflorescence consists of one or more 

 naked monoecious flowers borne on the edge or upper surface of the plant. Each 

 flower commonly consists of but a single stamen or a single flask-shaped pistil. 

 The anther has two to four pollen-sacs, containing spherical minutely barbellate 

 grains. The pistil is narrowed to the funnel-shaped scar-like stigmatic apex, and 

 produces 1-6 erect or inverted ovules. The fruit is a i 6-seeded utricle. 



Comprises the smallest of the flowering plants and contains 4 genera and about 26 species. 



Thallus with one root or several. 



1. Spirodela. 



2. Lemna. 



Roots several. 

 Root solitary. 

 Thallus rootless. 



Thallus thick, globose to subcylindric. 

 Thallus thin, ligulate. 



3. Wolffia. 



4. Wolffiella. 



i. SPIRODELA Schleid. Linnaea 13: 391. 1839. 



Thallus disc-shaped, 7-12-nerved. The thinly-capped rootlets as well as the nerves are 

 provided with a single bundle of vascular tissue. 

 Spathe sac-like. Anthers 2-celled. The ovary produces 

 two anatropous ovules. Fruit rounded, wing-margined. 

 [Greek, in allusion to the cluster of rootlets.] 



Two American species and S. oligorhiza, a native of 

 southern Asia, Australia and the Fiji Islands. The follow- 

 ing is the type of the genus. 



i. Spirodela polyrhiza (L.) Schleid. Greater 

 Duckweed. Fig. 1120. 



Lemna polyrhisa L. Sp. PI. 970. 1753. 



Spirodela polyrhiza Schleid. Linnaea 13: 392. 1839. 



Thallus round-obovate, 2"-s" long, thick, flat and 

 dark green above, slightly convex and purple beneath, 

 palmately 5-11 -nerved. Each thallus bears a cluster of 

 from 5-11 elongated rootlets. Rootcap pointed. 



In rivers, ponds, pools and shallow lakes, Nova Scotia to 

 British Columbia, south to South Carolina, Texas, north- 

 ern Mexico and Nevada. Also in Jamaica. Widely dis- 

 tributed in the Old World and in tropical America. Seldom 

 collected in flower. 



