24 FIELD AND FOREST. 



ered. Most common among the first is the Yellow Water-lily, or spat- 

 terdock {Nuphar advena), the Pickerel-weed {Pontederia cordata), 

 with cordate leaves like the Nuphar, but rather smaller, and with spikes 

 of purple flowers; the Peltandra also, with cordate erect leaves grow- 

 ing in clumps, and almost concealing its slender green spathes. Its 

 seeds are enclosed in a curious sack of jelly that swells enormously be- 

 fore germination ; they grow readily in a bottle. These three, with 

 the Zizania or Wild Rice (often miscalled reed-grass) are the prin- 

 cipal plants that cover the mud-flats. Scattered along the river-bank 

 are patches of the Orontium or Water Club, with oval, bright green 

 leaves, and spikes of small golden-yellow flowers with pure white stems. 

 Singly they are not conspicuous, but seen in masses on the water, they 

 are very beautiful. 



The White Water-lily is singularly rare about Washington, though 

 it is reported in Four-mile-run, half way to Alexandria, and the vari- 

 ety minor grows near Baltimore. Some of the Carices or Sedge-gras- 

 ses are occasionally found with the coarser plants we have mentioned, 

 though they usually grow near the water rather than in it. They are 

 well represented along the Potomac and its tributaries, more than six- 

 ty species, or one tenth of the whole number, being found here. 



Of the aquatic plants that live wholly in the water, all but five or six 

 belong to the Cryptogams— literally, a hidden marriage — plants with 

 flowers so small their separate parts cannot be distinguished by the na- 

 ked eye. The masses of long grass streaming with the current are 

 Valisneria or Eel-grass. Its staminate flowers grow under water, and 

 spontaneously break loose from their stems in August, and rise to the 

 surface to shed their pollen on the floating flowers of the opposite sex. 

 Accompanying this grass are long stems thickly set with little curly 

 willow-like leaves that give it a curiously crisped appearance as it is 



Plate i. — Phenerogams, Figure i. Potaniogeton lonchites, % natural size; 2, I'al- 

 lisneria spiralis, ^ natural size; 3. Anacharis alcinastrnnr, 4. Naiasflexilis; 5. Ccr- 

 atophyllon demersum, all natural size. Algse, (magnified), Figure 6. Pediastrum 



Boryanum; 7. Staurastriim dilatatuin\ 9. Sperogyra ; 10. Cosfnariiini cu- 



cumis; 12. Cosmarittiii ; 13. Merisinopeda nova; 16. Oscillatona, s"^. Ento- 



mostracEe (magnified). Figure 8. Bosmina longirostris; 14. Cyclops qiiadricontis. 

 Figures il. 17. 18. Diatoms magnified 55 diameters. Figure 15. Larva of Ephem- 

 era twice natural size. 



