RUPPIA.] NAIADES. 375 



1. R. maritima, L. ; leaves opposite and alternate. 

 Brackish ditches, &c. in England and Ireland, chiefly in the E. of Scotland ; 



fl. July-Sept. Habit of Potamogeton pectinatus. Stem filiform, much 



branched, 2 ft. and upwards. Leaves 1-3 in. ; stipules adherent and forming 



the leaf-sheath. Peduncle short and straight in flower, then lengthening to 



5-6 in. Drupe - in., green, beaked, pedicels 1-2 in. DISTRIB. All shores, 



temp, and trop. 

 Sub-sp. MARIT'IMA proper ; sheaths inflated, fruiting peduncles spirally coiled, 



anther-cells oblong, drupe nearly straight, beak short. R. spira'lis, Hartm. 



Yorkshire to Somerset ; rare in Ireland. 

 Sub-sp. HOSTELLA'TA, Koch (sp.); sheaths appressed, fruiting peduncles 



short flexuous, anther-cells subglobose, drupe gibbous, beak longer. 



Common ; flowers earlier. 



3. ZANNICHEL'LIA, L. HORNED POND-WEED. 



Slender water-plants. Leaves submerged, usually opposite, linear ; 

 stipules adherent to the sheathing leaf-base. Flowers minute, 1- or 2- 

 sexual, solitary or in pairs, sunk in the leaf-sheath. Perianth 0. Stameii 

 1 ; anther 2-celled, sagittate, cells adnate to the slender filament, dehis- 

 cence lateral, connective excurrent ; pollen globose. Ovary of 46 carpels 

 in a short sheath ; styles long or short, stigma peltate persistent ; ovule 

 pendulous, anatropous. Achenes 4-5, sessile or pe'dicelled, oblong, curved. 

 Seed pendulous, testa membranous ; radicle large, clavate ; cotyledon 

 slender, twice folded. DISTRIB. Temp, and trop.; species 1 or several. 

 ETYM. Zannichelli, a Venetian botanist. 



1. Z. palus'trls, L.; achencs curved, keel tubercled. 

 Fresh and brackish ditches and pools ; fl. May- Aug. Annual. Stem 3-6 in., 



filiform or setaceous ; branches divaricate. Leaves 1-3 in., opposite, sub- 



whorled, often capillary. Flowers sessile or shortly pedicelled. Acttene* 



narrow, ventral surface concave, dorsal convex. DISTRIB. Europe, N. Africa, 



Siberia, India. 

 Sub-sp. PALUS'TRIS proper ; ripe carpels subsessile spreading, dorsal face 



shortly winged and tubercled, style stout. Z. major, Hartm. 

 Sub-sp. PEDICELLA'TA, Fries (sp.) ; ripe carpels stipitate longer and narrower, 



dorsal face winged and tubercled, style long slender. 



A. ZOSTE'RA, L. GRASSWRACK. 



Grass-like marine plants ; rootstocks matted, creeping. Stem com- 

 pressed. Leaves distichous, sheathing, long, linear; stipules adherent to 

 the sheathing leaf-base. Flowers in 2 parallel series of alternating anthers 

 and ovaries on one surface of a linear membranous spadix, which is 

 enclosed in the sheath of a pedicelled leaf-like spathe. Perianth 0. 

 Antliers sessile, 1 -celled, dehiscence longitudinal ; pollen of simple slender 

 cells. Carpel 1, ovoid, fixed laterally ; style subulate, persistent, stigmas 

 2 capillary exserted from the spathe, deciduous ; ovule pendulous from 

 the point of attachment, orthotropous. Fruit membranous, dehiscing 

 vertically. Seed ovoid, testa tough ; embryo large, ovoid, with a small 

 uncinate subulate plumule in a lateral fissure. DISTRIB. Various coasts ; 

 species 2. ETYM. fear-rip, a riband. 



