naiadace^e. (pondweed family.) 431 



1. liEMNA, L. Duckweed. Duck's-jieat. 



Flowers appearing from a cleft in the edge of the frond, three together burst- 

 ing through a thin and membranous urn-shaped spathe ; two of them consisting 

 of single stamens (one developed rather earlier than the other), with thread-like 

 filaments and 2-celled anthers; the other a 1 -celled ovary forming a utricle in 

 fruit: stigma funnel-form : ovules anatropous or half-anatropous. — Root with 

 a sheath-like appendage on its extremity. Fronds laterally proliferous by a 

 sort of budding, and producing little bulbets which sink to the bottom of the 

 water in autumn but rise to develop on the surface in spring. (An old Greek 

 name, of uncertain meaning.) 



§ I. LEMNA, Schleiden. — Boot single : filaments filiform : ovule solitary. 



1. Ij. taissllCJS, L. Fronds oblong-lanceolate from a stalked base, thin, den- 

 ticulate at the tip (J'.-|' long), proliferous from the side, so as to form crosses; 

 " ovule half anatropous." — Ponds; not mrc : but the flowers little known. (En.) 



2. Jj. IBIIIIOI', L. Fronds roundish-obovate, thickish (about 2" long), 

 often grouped ; " ovule half-anatropous : seed horizontal." — Very common, man- 

 tling stagnant waters : not yet found in flower in this country. (Eu.) 



3. L.. pcrpSiSUIa, Torr. Fronds obova-te, thin (l"-H"long), single or 

 grouped ; ovule anatropous ; seed erect, striate. — Staten Island, New York ( Tor- 

 rey), and doubtless common elsewhere. August. 



§ 2. SPIRODELA, Schleiden. — Roots several in a cluster from each frond: fila- 

 ments of the stamens narrowed below : ovules 2. 



4. L. polyri'hlzn, L. Fronds roundish-obovate (3" -4" long), thick, 

 rather convex beneath. — Ponds and pools. Sometimes found in flower. (En.) 



§3. TELMAT6PHACE, Schleiden. — Roots single: filaments of the stamens 

 enlarged in the middle : ovules and seeds 2-7, anatropous : albumen little. 



5. JL. gibl)U, L. Fronds obovate, nearly flat above, tumid and spongy under- 

 neath (hemispherical), proliferous on short and very fragile stalks, therefore 

 seldom found connected (3"-4"long). — Ponds; rather rare. Not here seen 

 in flower. (Eu.) 



Order 115. NAI ADACEiE. (Pondweed Family.) 



Immersed aquatic plants, with jointed stems and sheathing stipules toiffiin 

 the petioles, or with sheathing bases to the leaves, inconspicuous mono — dioe- 

 cious or perfect flowers, which are naked or icith a free merely scale-like calyx ; 

 the ovaries solitary or 2-4 and distinct, 1-celled, 1-ovuled. Seed without al- 

 bumen, filled by the large embryo, often curved or hooked. Flowers usu- 

 ally bursting from a spathe, sometimes on a spadix. 



Synopsis. 



# Flowers monoecious or dioecious, axillary, naked, monandrous. 



1. NAIAS. Pistils solitary and naked : stigmas 2-4 



2. ZANNICHELLIA. Pistils about 4 from a cup-shaped involucre or sheath. 



