LIFE IN PONDS AND STREAMS 



in air. Among them are reeds, bulrushes, and marsh grasses, 

 the white-blossomed arrowheads, water plantains, the massed 

 blue spikes of the pickerel weeds, and crowding into every 

 space high standing-armies of cat-tails (Fig. 17). Covering 

 their stems below the water line are the simpler plants, 

 desmids and other algae, on which swarms of small crusta- 

 ceans feed. Little plant-eating worms are abundant on them, 

 also, and some of the smaller water beetles. 



Beyond this zone are the floating-leaved plants, growing 

 in water knee-deep or a little more. There, the bottom is 



Fig. 18. — Diagram showing the population on the 

 undersides of lily pads: i, bryozoan colony; 2, midge 

 larva; 3, snail's eggs (Physa); 4, beetle's eggs (Dona- 

 cia); 5, snail (Grauhis); 6, snail (Physa); 7, eggs of 

 caddis fly {Tricenodes); 8, water-mite; 9, tubes of 

 midge larvae; 10, eggs of water-mite; 11, eggs of 

 damselfly (Enallagma); 12, tube of rotifer (Melicerta); 

 13, sponge; 14, eggs of whirligig beetle. 



soft and pleasant to walk through and the mud boils up 

 through it with every step one takes. Near shore, lily pads 

 and the ever-present little duckweeds lie on the surface 

 and leaves of the yellow spatterdocks are only half lifted 



13 



