PLANKTON ALG OF LAKE ERIRF. 315 
The dimensions are 10.5 to 13 “ long and 6.5 to 8 “ broad. The color is a brighter and yellower 
green than that of the preceding species; the pyrenoid, instead of being at the extreme posterior 
end of the cell is near the center, and the pigment spot is an inconspicuous elongated strip of dull 
red which can rarely be distinguished, except when viewed at the side. In all other respects the 
structure of this species resembles that of the preceding. The division is longitudinal. Chlamydo- 
monas communis, though in general appearance greatly resembling Chlamydomonas media Klebs, 
is smaller, the largest cells being only about half as large as the largest of that species. The mode 
of division also in the two species is so different that the two could not be classified together. 
This species was found in many collections taken at the western end of Lake Erie. 
Chlamydomonas globosa Snow, new species. 
In the natural condition in the plankton of Lake Erie this species exists abundantly, but in a 
form not easily recognized as a Chlamydomonas. In appearance it resembles Plewrococeus regu- 
laris Artari, consisting of one or more clusters of spherical cells, more or less separated from each 
other, and all imbedded and held in place by a thick, gelatinous covering. When first placed in 
culture the gelatinous envelope disappears, the cells become isolated and the normal appearance of 
a Chlamydomonas is assumed; but when division occurs the alga takes again the cluster form as 
found in the plankton. 
In the motile form the cells are spherical or slightly ellipsoidal, with a diameter of 5 to 7.8 w. 
No anterior beak is present. There are two flagella, as long or slightly longer than the cell, and 
a small inconspicuous pigment spot at the side, about half way between equator and cilia (fig. ur). 
The chloroplast extends to the extreme anterior end of the protoplast, and is much thickened 
at the posterior end, in which portion the pyrenoid lies. The pyrenoid is enveloped by a thick 
layer of starch. Only a single pulsating vacuole can be distinguished at the anterior end, but this 
is unusually large in size. Several globules of oil are present in the anterior portion of the cell. 
Often the cell contents are withdrawn from the membrane, either at the anterior end, the posterior 
end, or at all points. Gametes were not found. 
After division the cells are liberated by the cell wall becoming gelatinous. In 0.2 per cent 
Knop’s solution, where division took place normally and rapidly, the cells existed in clusters of 
four, which resembled in every respect some of the cell compounds found in the plankton. This 
species of Chlamydomonas was cultivated for a period of two years, and during this time no 
variation was noticed. 
Scenedesmus bijugatus var. flexuosus Lemm. 
The form under consideration is identical with Scenedesmus bijugatus var. flecuosus described 
by Lemmerman ’99, except that in a ccenobium 32 cells seem to occur more frequently than 16 
(fig. 1v,1). Both numbers frequently appear in the plankton of Lake Erie, however, and the 
two forms are undoubtedly the same. This variety was cultivated by the author for about a year 
under a large number of conditions, and as some points were observed, not noted in Lemmerman’s 
description, they are given here. 
It was first thought from its general resemblance to S. bijugatus that it might be this species 
which had assumed a greater development due to unobstructed light and the inexhaustible supply 
of oxygen. carbon dioxide, and nutritive substances which are constantly supplied by the ever- 
moving water of the lake, but cultivation of the species for some months, during which many 
generations were traced, proved that the great number of cells was characteristic for the organism, 
and that when placed under the artificial conditions, where the supply of air and nutrition were not 
so constantly renewed as in the lake, it did not necessarily revert to the usual form of S. bijugatus 
with 8 cells. It is true that. under special conditions, where the vitality was low, it sometimes 
produced an 8-celled ccenobium, but in the same culture where 8 cells were found ccenobia of 16 
or 32 cells were also found. The ccenobia of 8 or 16 cells produced again ccenobia of 32 cells, so 
that it would seem that the larger number of cells was normal, rather than abnormal. 
The greatest diameter of the cells of a mature coenobium is 20.8 4, while the shortest is 8.9 u. 
A young coenobium of 32 cells measured 160 in length, while an older one measured 364 “. The 
great length of one of these individuals strongly suggests a filamentous alga. The shape of the 
cells in young ccenobia is cylindrical, with slightly rounded ends. In older individuals which are 
