NAIADACK^. (PONDWEED FAMILY.) 483 



1. M". mkjOV, All. Leaves linear, rather broad, strongly rcpand-toothed, 

 the back as well a> the stern more or less beset with little spines, the sheathing 

 base entire or nearly so; flowers dioeeious ; antlur 4-cclled, 4-valved. — New 

 York, Onondaga Lake, G. ^F. Clinton ; Lake Ontario, near Roehester, C. M. 

 Booth: recent discoveries. (Eu.) 



2. N. flexilis, liostk. Leaves very narrowly linear and minutely serrate, 

 as is their alniiiit rounded sheathing base ; flowers monoecious ? (N. Canadensis, 

 Michx. Cauliuia flcxilis, ]Villd.) — I'onds and slov.' 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- 

 cclled anther; the fertile of 2-.'j (usually 4) sessile pistils in the same cup- 

 shaped involucre, forming obliquely oblong nutlets in fruit, beaded wuh a short 

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

 Seed oithotropous, suspended, straight. Cotyledon taper, bent r--id coiled up. 

 — Slender branching herbs, growing under water, with opposit-^ or alternate 

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

 (Named in honor o? Zanniclie/li, a Venetian botanist.) 



1. Z. paltistris, L. Style at least half as long as the fn-it, which is flat- 

 tish, somewhat incurved, even, or occasionally more or less top*hed on the back 

 (not wing-margined in our plant), nearly sessile ; or, in var. PEruvcuLXxA, both 

 the cluster and the separate fruits evidently pedunclcd. — -.Vuds and slow 

 streams: rather rare. July. (Eu.) 



3. ZOSTERA, L. Gr.\ss-avkack. EEr crass. 



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

 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 (spatiie) ; the sterile flowers consist- 

 ing of single ovate or oval 1-celled sessile anthers, as large a? the ovaries, and 

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

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

 shaped style, and containing a pendulous orthotropous ovule : r>tigmas 2, long 

 and bristle-form, deciduous. Utricle bursting irregularly, enclcsing 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 'eaves 

 (whence the name, from ^coarijp, a hiind). 



1. Z. marina, L. Leaves obscurely 3-5-nerved. — Common :r. htys 

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



4. RIJPPIA, L. Ditch-grass. 



Flowers perfect, 2 or more apjiroximated on a slender spadix, which 'S at first 

 enclosed in the sheathing spathe-like base of a leaf, entirely destitute <>f flu/^h 



