122 
UROGLENOPSIS AMERICANA IN WINDERMERE. 
W. H. PEARSALL, D.Sc.„ F.L.S. 
In July and August, 1932, the water of Windermere contained 
very large numbers of an alga which proved on examination 
to be Uroglenopsis americana (Calkins) Lemmerman. The 
alga was composed of a colourless, gelatinous matrix of 
spherical shape, on the outside of which were embedded 
ellipsoidal cells. Each cell was provided with an eye spot 
and a single golden-brown to olive-brown chromatophore. 
The latter was plate like or disciform. Globules of an oily 
nature were present. Protruding through the gelatinous 
matrix into the outer water from each cell were two cilia of 
unequal length, the longer about two to three times the 
length of the cell, the shorter about half the length of the 
cell or rather less. The cells were about 6 — 10^ in length, 
and the colonies were between 300 and 400 /i in diameter. 
The plant is excellently figured by G. M. Smith (Wisconsin 
Phytoplankton, Wise. Geol. and Nat. Hist. Survey, No. 57, 
1920). 
This species has not been described previously for the 
British Isles, although it is recorded for Germany. It is not 
impossible, however, that it has been missed because I found 
it impossible to preserve it for subsequent examination. 
Within an hour or two after making a collection almost all 
the colonies were unrecognisable. The individual cells shoot 
out from the gelatinous matrix and swim round independently 
in the external medium for a time before settling down and 
losing their cilia. In cultures they showed no disposition to 
form new colonies. The same disorganisation takes place 
immediately preservatives are added, and none out of a large 
number of methods of fixing algae was successful in preserving 
any of the colonies for more detailed examination. 
On account of this peculiarity it is not easy to say whether 
Uroglenopsis americana is a species newly established in 
Windermere or not. In view of the rapidity with which it 
disorganises it is quite possible that it may have been present 
in previous years in smaller numbers and have escaped notice. 
Most of the earlier collections recorded from this lake were 
not examined until an hour or two after collection. I feel 
fairly safe in saying, however, that Uroglenopsis could hardly 
have escaped detection if it had been present in earlier years 
in the numbers in which it was present in 1932. It was 
immediately obvious to the naked eye, and the peculiar 
olive or brownish tinge of the colonies was immediately 
noticeable, so that even without a microscope it would not 
have been possible to mistake it for a green or blue-green 
algae. 
The Naturalist 
