86. NAIAD ACE^E. 173 



9. P. RUFESCENS, Schrad. Reddish Pondweed. Floating le. 

 on short stalks, coriaceous, oblong or lanceolate, lower or sub- 

 merged le. lanceolate, tapering at both ends, not apiculate, with 

 chain-like network at the midrib. Stipules not winged. Ped. not 

 thickened upwards. A much larger plant than the last, with the 

 upper le. tinged with red. 



Not common. Canals and ditches. (B) P. 7. Possil marsh ; Forth and Clyde 

 Canal, &c. 



10. P. NATANS, L. Broad-leaved Pondweed. Moating le. 

 elliptical, 4 5 in. long, coriaceous with numerous veins, on long- 

 stalks, submerged le. linear, thin, often wanting. Stipules 

 closely sheathing, very large. Ped. thick. Spike cylindrical, 

 dense. Nuts large, keeled when dry. The le. become elongated 

 and narrow in rapid streams. 



Common. In rivers and stagnant water. (B) P. 6 7. Frankfleld, Hoggan- 

 field, Bardowie, and St. Germans lochs; Cumbrae and. Arran. 



11. P. OBLONGUS, Viv. Oblong-leaved Pondweed. Known 

 better from the last by its size than by any characters that can 

 be given to it, being always small. Upper le. oblong-elliptical, 

 lower le. linear, often absent. Ped. equal. Spike dense. Nut 

 small, faintly keeled when dry. 



Common. In ditches nearly dry in summer, and on the surface of peat bogs. 

 (B) P. 7. Possil marsh; Cathkin hills ; Frankfield and Hogganfield lochs ; Gourock 

 to Arran. 



2. ZANNICH^LLIA. Horned Pondweed. 



Z. PALUSTRIS, L. Stems long, slender, branched, and floating. 

 Le. opposite, linear, entire, with a small membranous sheathing 

 stipule. Fl. axillary from a membranous bract. Fertile ones 

 shortly stalked. St. with a long white filament. Nut when ripe 



ten with a toothed keel. 



Rare. Rivers and ditches. (B) A. 5 8. " In the Clyde near the ford, Bogle's 

 hole," llopJc. "Below Hamilton bridge," Patr. Forth and Clyde Canal beyond 

 Kilsyth. 



3. ZOST^RA. Grass-wrack, "Alva-marina" 



1. Z. MARINA, L. Broad-leaved Grass-wrack. Rhizome creep- 

 ing. Le. flat, long, linear, 3 5-veined, sheathing at the base. 

 Flower-bearing le. with a sheathing spatha covering the fl. and 

 spadix. "Ped. of the spatha thick, shorter than the spadix." 

 Fl. in 2 rows. St. and pistils alternate. Fruit striate. 



Var. augustifdlia, le. narrow, short, 1 3- veined. " Ped. of the 

 spatha slender, as long as, or longer than, the spadix," H. & A. 



Very common. In the sea, and on banks at low water. (B) P. 7 8, The 

 fibre of the le. has been proposed as a substitute for cotton. The narrow form on 

 mud banks and in salt water ditches. 



