NAIADACE^. (PONDWEED FAMILY.) 483 



1. N. m^jor, All. Leaves linear, rather broad, strongly repand-toothed, 

 the back as well ai the stem more or less beset with little spines, the sheathing 

 base entire or nearly so; flowers dicEcious; anther 4-celled, 4-valved. — New 

 York, Onondaga Lake, G. W. Clinton ; Lake Ontario, near Rochester, C. M. 

 Booth: recent discoveries. (Eu.) 



2. N. fl6xilis, Rostk. Leaves very narrowly linear and minutely serrate, 

 as is their abrupt rounded sheathing base ;■ flowers monoecious f (N. Canade'nsis, 

 Michx. Caulinia flexilis, Wilid.) — Ponds and slow streams : common. (Eu.) 



2. 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 up. 

 — Slender branching herbs, growing under w.ater, with opposite or alternate 

 long and linear thread-form entire leaves, and sheathing membrapous stipules. 

 (Named in honor of Zannichetti, a Venetian botanist.) 



1. Z. paMstris, 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. pedunoulXta, both 

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

 streams: rather rare. July. (Eu.) 



3. ZOSTERA, L. Gkass-wkack. Eel-grass. 



Flowers monoecious ; the two kinds naked and sessile and alternately arranged 

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

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

 ing 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, growing 

 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 (axTrrip, a band). 



I. Z. marina, L. Leaves obscurely 3-5-nei-ved. — Common in bays 

 along the coast, in water of 5° - 15° deep. Aug. (Eu.) 



4. RUPPIA, L. DiTca-SRASs. 



Flowers perfect, 2 or more approximated on a slender spadix, which is at first 

 enclosed in the sheathing spathe-like base of a leaf, entirely destitute of floral 



