THE BOTTLE ANIMALCULE, FOLLICULINA. 265 



The Elodea generally grows in a dense continuous plantation 

 the crowded tops almost touching, so that in a square foot there 

 is at least one plant with some fifty leaves on its upper four 

 inches where the Folliculina tubes abound; on an average each 

 leaf has five to ten tubes; many have much greater numbers. 

 Allowing 250 tubes to the square foot, which is a minimum 

 estimate for the more sparsely populated regions, and estimating 

 the length of the Elodea zone as twenty miles and its width as 

 only 4 feet, since the Folliculina are most abundant in water 

 3-4 feet deep and not in the upper and lower edges of the Elodea 

 zone, we would have some one hundred million of these miniature 

 dwellings along the Severn. They were found also in abundance 

 at the head of Whitehall river which opens independently into 

 the Chesapeake just to the north of the Severn, and as they are 

 probably widely distributed along the branches of the Chesapeake 

 we may regard Folliculina as a numerically important member of 

 the summer fauna of this large body of salt water. 



The following experiments throw light upon the distribution 

 of the tubes of Folliculina in various depths of water. Late in 

 July with water at 28 C. strips of smoothly sawed pine wood 35 

 mm. wide and 9 mm. thick were stuck upright in the mud in a 

 row across the Elodea zone and left six days. On all strips in 

 from two feet to five feet depth of water many tubes of Follicu- 

 lina were attached, but they were absent from the bottom for 

 some eight to twenty inches above the mud and from the top 

 some nine inches below high tide line. The stick nearest shore 

 in two feet water had a sparse population, perhaps 100 tubes to 

 the square inch, while the sticks farther out showed in places 

 as many as 400 per sq. inch. In these latter the tubes were 

 often aggregated in clusters, one containing as many as 73 tubes, 

 while in the more shallow water the tubes were scattered and 

 more irregular in distribution. To see if the tubes would be 

 made in depths beyond the Elodea zone the same strips of wood 

 were tied together in a row, end to end, and anchored in the 

 middle of the mouth of a creek where there was no plant life on 

 the bottom, the water being 15 feet deep, and the Elodea zone 

 several hundred feet distant. After a submergence of three 

 days and four nights all the four sections of the compound strip 



