302 SYSTEMATIC BOTANY. 



pound ovary of 3-6 cells. Stigmas sessile. Capsule dividing at length 

 into 3-6 i-seeded carpels. 



T. MARITIMUM (Arrozv-grass). Scape naked, fleshy, angled ; leaves 

 very narrowly linear, fleshy, semi-cylindric, shorter than the scape ; flowers 

 small, green, pedicellate, arranged in a long, loose raceme, destitute of bracts ; 

 fruit ovate, composed of 6 carpels, rounded at base. In salt marshes, 8'-i5' 

 high. August, y. 



Order LXXXIII. NAIAD ACE^E (Pondweed Family). 



Aquatic plants, with cellular leaves. Flowers inconspicuous, 

 perfect, monoecious, or dioecious. Perianth of 4 distinct sepals, 

 rarely monosepalous. Stamens definite, 4, 2, or I. Ovaries I ; or 

 else 2-4, free from the perianth, distinct. Stigma simple, often 

 sessile. Fruit I -celled, I -seeded, indehiscent. 



( Flowers perfect Potamogeton. 

 ( Flowers imperfect Naias. 



1. Naias. Flowers monoecious or dioecious, axillary, solitary. Bar- 

 ren flowers stamen I, in a little spathe. Fertile style I, short ; stig- 

 mas 2-4 ; ovary I. Achenium i-seeded, in a loose, membranous 

 sheath. 



N. FLEXILIS ( Water Nymph}. Aquatic ; stem very slender, dichoto- 

 mously branched ; leaves opposite or whorled, very narrowly linear, sheath- 

 ing at base ; flowers minute, axillary. In ponds and slow waters. Stem 

 5'-2o' long. July-September. 



2. Potamogeton. Flowers perfect, spicate. Sepals 4. Stamens 

 4. Anthers 2-celled. Ovaries 4. Achenia 4, sessile, flattened on the 

 inner side. Floating aquatics. 2{ 



1. P. NATANS {Broad-leaved Pondweed). Stem nearly or quite simple ; 

 upper leaves ovate or broadly elliptical, varying to oblong-lanceolate, rounded 

 or cordate at base ; immersed ones lanceolate, linear or capillary, all on long 

 petioles ; spike of purplish flowers raised above the water. Ponds and slow 

 waters. July-September . 



2. P. GRAMINEUS (Various-leaved Pondweed). Stems slender, mostly 

 branched below ; upper leaves oval, on long petioles ; immersed ones lanceo- 

 late, varying to narrow-linear, or even capillary ; lower ones sessile ; spikes 

 cylindrical, somewhat loose, on long peduncles thicker than the stem. Com- 

 mon in shallow, stagnant, and slow waters. July-August. 



3. P. PERFOLIATUS (Clasping Pondweed). Stem branching dichoto- 

 rnously ; leaves alternate, ovate, sometimes broad-ovate, obtuse, cordate and 

 clasping at base ; spike purplish, loosely-floweredj on a short peduncle, 

 July- A ugust. 



