Marsh Animals 345 



joint weed (Polygonum) and the buck-bean (Menyan- 

 thes trifoliata). True climbers also, are present in the 

 marsh although usually only on its borders; such are 

 the climbing nightshade bittersweet (Solanum dulca- 

 mara) and the beautiful fragrant -flowered climbing 

 hemp-weed (Mikania scandens). Here and there one 

 may see a protruding top of swamp dock (Rumex 

 verticillatus) , a water hemlock (Cicuta bulbifera) or a 

 swamp milkweed (Asclepias incarnata). 



Every opening in the marsh contains forms that are 

 more characteristic of ponds and ditches, such as arrow- 

 heads and water plantain. And even the little trash 

 filled pools often contain their submerged aquatics. 

 Such a one is shown in the figure 203, a shallow pool 

 filled with fallen leaves, its surface suddenly sprinkled 

 over with little star-like flowers when the white water- 

 crowfoot shoots up its blossoms. 



Algae often fill these pools; sometimes minute free- 

 swimming forms that tint their waters, but more often 

 "blanket algae," whose densely felted mats may smother 

 the larger submerged aquatics. 



The animal life of the marsh is also a mixture of pond 

 forms and of forms that belong to the more permanent 

 waters. The fishes are bullheads and top minnows and 

 others that can endure foul waters, scanty oxygen and 

 rapid fluctuations of temperature. Of crustaceans, 

 ostracods and scuds are most abundant. Of molluscs, 

 Pisidium and Planorbis are much in evidence, and other 

 snails are common. Insects abound. Some are aqua- 

 tic and some live on the plants. Of all Odonata, Lestes 

 (fig. 204) is perhaps the most characteristic marsh inhabi- 

 tant ; of mayflies, Blasturus and Caenis ; stoneflies, there 

 are none. Of caddis-flies there are many, but Limno- 

 philus indivisus is perhaps the most characteristic marsh 

 species. It is not known to inhabit any waters except 



