THE BOTTLE ANIMALCULE, FOLLICULINA. 269 



In the general process of capture of fresh by marine biota, 

 may be included the temporary utilization of the fresh water 

 plants, Elodea, Potamogeton, etc., by the summer immigrants 

 from the sea. The swarms of Folliculina settling in the Elodea 

 zone is but one illustration of the push from the sea inland. 



The waters of the Severn support a thousand acres of natural 

 oyster bars and are thus marine rather than freshwaters. The 

 water in this river as published in 1912 by the Shell Fish 

 Commissioners of Maryland varied from 1.0036, 1.0048 in 

 July to i.on in December and 1.0096 in March; the gravity of 

 the ocean being from 1.025 to 1.027. It should be emphasized, 

 however, that each creek has some little spring or stream of 

 fresh water entering its head as representative of the former head- 

 waters of a side branch of the original fresh stream and where 

 this water meets the saline tide waters there is an oscillation of 

 conditions from the densities of high tides in dry seasons to the 

 extreme freshness of low tides and in-pour of torrents of muddy 

 water after rains. It is between these oscillation areas on the 

 one hand and the more continuously saline depths on the other 

 that the Elodea zone is most pronounced. 



By July 4, Folliculina was very abundant over the leaves of 

 Elodea in small scattered colonies of each a few individuals; by 

 the 1 3th, exceedingly abundant on most all the leaves of the top 

 two to four inches of Elodea in two to four feet depths in a zone 

 12 feet wide; they also formed a black area a few inches wide 

 close to the surface of the water along the sides of a floating boat, 

 twenty feet from the Elodea zone. 



With the progressive growth of Elodea the upper leaves are 

 the only ones upon which live Folliculina is found while the older 

 leaves are thick-set with empty tubes. As the plant grows 

 upward the shaded old leaves macerate and disappear but the 

 tubes fall off to the bottom and may be got in great numbers 

 from the mud as well as from the macerated dead leaves. In 

 August, Elodea may be four feet high, but only the upper foot 

 has leaves, and on these the dense settlements of Folliculina are 

 generally a few inches from the top. Examination of the leaves 

 shows the youngest Folliculinas on the uppermost or youngest 

 leaves and so on down. Thus during the growing season there 



