268 E. A. ANDREWS. 



patches I to 2 mm. in diameter here and there on the leaves of 

 Elodca in water two to six feet deep, otherwise the leaves were 

 clean. These patches or colonies of FolUculina were only one 

 to the leaf, either at the tip or at the edge of the upper surface. 

 The origin of these first tubes was not determined. Aquaria 

 that contained FolUculina in the fall still contained the empty 

 tubes at this season but no revival of FolUculina was found in 

 the aquaria even though the aquaria were kept all the summer. 



Whether the FolUculina passes the winter in some form in the 

 mud to develop when the conditions are right or whether it 

 migrates into the river each season and becomes attached when 

 the growth of the plants, the temperature and food conditions 

 permit, is not known. The fauna of the Bay and river is markedly 

 increased by migrants; not only are there vast shoals of jelly-fish 

 (Chrysaora form of Dactylometra} and of ctenophores that come 

 and go with menhaden and other fish but the plants that grow 

 along the shores become the support for bacteria, diatoms, 

 protozoa, anemones, polyzoa, tunicates and nudibranchs, that 

 disappear in the fall and seem to have arrived as plankton and to 

 have multiplied or grown in the temporary forcing house that 

 this body of water forms in the summer. With the water gradu- 

 ally becoming opaque green from the multiplication of the micro- 

 scopic biota and the temperature running up to 27 to 30 C. in 

 July when the air is 28 to 29 C. FolUculina with many other 

 organisms lives in ideal conditions for rapid multiplication, so 

 that a few immigrants from the sea might produce the entire 

 population that dies out at the oncoming of cool weather and 

 the great changes in the gross and microscopic fauna and flora 

 of the shores. Thus FolUculina and other marine animals become 

 temporarily associated in a summer community dependent upon 

 the zones of essentially fresh water plants, Elodea and Pota- 

 mogeton. 



The Chesapeake and its branches is a typical "drowned river" 

 and we find here a tendency toward a gradual capture of the fresh- 

 water biota by the incoming marine biota. Thus the marine 

 blue-crab with many sea fish migrates over the line between 

 the fresh and salt waters and at times becomes an important 

 factor in the cecology of fresh and of marine organisms as well 

 as of the dwellers on the transition line. 



