MONOCOTYLEDONOUS OK ENDOGENOUS PLANTS. 529 



anther 2-cellecl, on a long and slender filament; aclienia 

 3-0 in a cluster, commonly raised on a short common pe- 

 duncle, each stalked, linear-oblong, somewhat compressed 

 and curved, smooth and wingless, about one-third longer 

 than the persistent style. Fresh or brackish water. May- 

 August. Stems l°-3° long; leaves l'-2' long. 



RUPPIA, L. Ditch Grass. 



Flowers perfect, naked, two or more on a slender spadix, 

 inclosed in the spathe-like sheaths of the leaves, but soon 

 long-exserted ; stamens 2, closely sessile ; a?ither-ce\ls large, 

 distinct; ovaries 4, sessile, containing a single suspended 

 campylotropous ovule; stigma peltate; acheniicm stalked, 

 obliquely ovate ; embryo pointed by the short plumule. — 

 Salt-water herbs, with filiform branching stems, and alter- 

 nate linear or bristle-like sheathing leaves. 



R. MARiTiMA, L. In shallow water, along the coast. 

 May-August. Stems immei-sed, l°-3° long, mostly creep- 

 ing at the base; leaves filiform, l'-3' long, with dilated 

 membranaceous sheaths; fruiting peduncles 1-4' long; 

 achenium pointed. 



POTAMOGETON, Tourn. Pondweed. 



Floivers perfect, spiked ; sepals 4, roundish, valvate in 

 the bud ; stamens 4, opposite the sepals ; filaments short ; 

 anthers 2-celled; ovaries 4, sessile; ovules ascending, cam- 

 pylotropous; ^///?e short or none; stigma ^Q\t2Lie', achenia 

 1-4, compressed ; embryo curved or coiled. — Aquatic herbs, 

 with immersed slender and jointed stems ; leaves stipulate, 

 alternate and opposite, either all immersed and commonly 

 membranaceous, or the upper ones floating and more rigid ; 

 sjnJces peduncled, axillary and terminal. 



* Leaves all immersed and alike. 



t Leaves lanceolate or cordate; stipules free, sheathing. 



P. PERFOLIATUS, L. Stem terete, branching, very leafy ; 



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