NAIADACE^E. (PONDWEED FAMILY.) 565 



5. ZANNICHELLIA, Micheli. HORNED PONDWEED. 



Flowers monoecious, sessile, naked, usually both kinds from the same axil ; 

 the sterile consisting of a single stamen, with a slender filament bearing a, 2 - 

 4-celled anther ; the fertile of 2 - 5 (usually 4) sessile pistils in the same cup- 

 shaped involucre, forming obliquely oblong nutlets in fruit, beaked with a short 

 style, which is tipped by an obliquely disk-shaped or somewhat 2-lobed stigma. 

 Seed orthotropous, suspended, straight. Cotyledon taper, bent and coiled. 

 Slender branching herbs, growing under water, with mostly opposite long and 

 linear thread-form entire leaves, and sheathing membranous stipules. (Named 

 in honor of Zannichelli, a Venetian botanist.) 



1. Z. pallistris, L. Style at least half as long as the fruit, which is flat- 

 tish, somewhat incurved, even, or occasionally more or less toothed on the back 

 (not wing-margined in our plant), nearly sessile; or, in var. PEDUNCUL\TA, 

 both the cluster and the separate fruits evidently peduncled. Ponds and slow 

 streams, throughout N. America, but not common. July. (Eu., Asia.) 



6. ZOSTER A, L. GRASS-WRACK. EEL-GRASS. 



Flowers monoecious; the two kinds naked and sessile and alternately ar- 

 ranged in two rows on the midrib of one side of a linear leaf-like spadix, which 

 is hidden in a long and sheath-like base of a leaf (spathe) ; the sterile flowers 

 consisting of single ovate or oval 1 -celled sessile anthers, as large as the ovaries, 

 and containing a tuft of threads in place of ordinary pollen ; the fertile of single 

 ovate-oblong ovaries attached near their apex, tapering upward into an awl- 

 shaped style, and containing a pendulous orthotropous ovule ; stigmas 2, long 

 and bristle-form, deciduous. Utricle bursting irregularly, enclosing an oblong 

 longitudinally ribbed seed (or nutlet). Embryo short and thick (proper cotyle- 

 don almost obsolete), with an open chink or cleft its whole length, from which 

 protrudes a doubly curved slender plumule. Grass-like marine herbs, grow- 

 ing wholly under water, from a jointed creeping stem or rootstock, sheathed 

 by the bases of the very long and linear, obtuse, entire, grass-like, ribbon-shaped 

 leaves (whence the name, from fwtmfjp, a band). 



1. Z. marina, L. Leaves obscurely 3-5-nerved. Common in shoal 

 water of bays along the coast, from Newf. to Fla. (Eu.) 



7. NAIAS, L. NAIAD. 



Flowers dioecious or monoecious, axillary, solitary and sessile ; the sterile 

 consisting of a single stamen enclosed in a little membranous spathe ; anther at 

 first nearly sessile, the filament at length elongated. Fertile flowers consisting 

 of a single ovary tapering into a short style ; stigmas 2-4, awl-shaped ; ovule 

 erect, anatropous. Fruit a little seed-like nutlet, enclosed in a loose and separ- 

 able membranous epicarp. Embryo straight, the radicular end downward. 

 Slender branching herbs, growing under water, with opposite and linear leaves, 

 somewhat crowded into whorls, spinulose-toothed, sessile and dilated at base. 

 Flowers very small, solitary, but often clustered with the branch-leaves in the 

 axils; in summer. (Nai'cb, a water-nymph.) 



1. N". marina, L. Stem rather stout and often armed with broad prickles ; 

 leaves broadly linear (3 - 18" long), coarsely and sharply toothed, the dilated base 

 entire ; fruit 2 - 2-J-" long ; seed very finely lineate, oblong, slightly compressed 



