APETALOUS EXOGENOUS PLANTS. 479 



PODOSTEMON, Michx. River-weed. 



Spathe 2-leavecl ; floiuers pediceled ; filaments elongated, 

 borne on one side of the stalk of the ovary, united below, 

 and bearing only a single anther ; styles 2, simple ; capsule 

 ribbed, 2-celled, 2-valved; seeds imbricated. — Submerged 

 aquatic plants, attached to rocks and pebbles by disk-like 

 expansions of the stem ; leaves 2-ranked, divided into fili- 

 form segments. 



P. CERATOPHYLLUM, Michx. LeavBs rigid, sparingly 

 divided, sheathing at the base ; floiuers solitary, on slender 

 pedicels; capsule oval, 8-ribbed. Rocky places in rivers. 

 July. Plant olive-green, l'-4' long. 



P. ABROTANOIDES, Nutt. Leaves much divided, with 

 hair-like segments ; floiuers 2-3 together, on short pedicels; 

 capsule oblong, 10-ribbed. Gravelly places in rivers. — 

 Nuttall. Plant larger than the last. 



111. SPURGE FAMILY. Order, Euphorbiace^. 



Plants commonly with acrid milky juice, and monoecious 

 or dioecious oheii 2:)etalous floiuers ; calyx 2-8-lobed, mostly 

 valvate in the bud, sometimes wanting ; stigmas 2-several, 

 simple or divided; fruit of 2-several (mostly 3) 1-2-seeded 

 carpels united around a central axis, separating at matu- 

 rity, rarely 1-celled or indehiscent ; seeds suspended, ana- 

 tropous ; embryo in fleshy albumen ; cotyledons flat. 



SYNOPSIS. 



§ Ovules and seeds solitary in the cell ; flowers moruecious. 

 * Flowers without floral envelopes, inclosed in a common cup-shaped involucre. 

 Fertile flowers solitary in the l-5-toothed involucre. Sterile flowers several, each reduced 

 to a single stamen Ettphobbia. 



** Flowers in bracted spikes or racemes ; the upper ones sterile, Vie lowest fertile. 

 t Flowers apetalous. 

 tt Stigma and cells of the capsule 6-7. 



Calyx 2-Z-toothed. Anthers erect. Staminate flowers clustered Stiijjngia. 



Z-parted. pendulovs, Staminate flowers single ExcffiCiJUA. 



