PLANKTON ALG OF LAKE ERIE. 379 
A distinguishing character is the gelatinous covering, usually about 6.5 to 8 /« thick, surrounding 
each cell. This is excreted from the cell and is of such a consistence as to be plainly visible 
under the microscope, but shows no laminated structure. In mature cells no further structure is 
visible in the gelatinous substance; but in rather young individuals, if cells be stained with tannate 
vesuvine, and sometimes without staining, two portions of the ruptured mother membrane are 
seen lying imbedded in this gelatinous substance (fig. v1, 4). 
The membrane of the cell is composed of cellulose , which shows the blue color with iodine 
and sulphuric acid. The gelatinous envelope remains unaltered in appearance with these 
reagents. The chloroplast occupies the larger portion of the cell, leaving near the center only a 
relatively small space, which in direct view appears as a lighter circle. In this lies the nucleus. 
A large pyrenoid is prominent, lying also near the center of the cell. Small globules of oil occur 
and become darkened by osmic acid. In old cultures the cell assumes something of a brownish 
color, which may represent a resting stage, but when such a brownish cell was allowed to dry it 
could not be induced to grow again. 
The reproduction takes place by a single transverse division of the contents of the mother cell 
(fig. vi, 1. 2). The two parts thus formed gradually elongate in opposite directions from the 
point where division took place, one slipping by the other in the process (fig. v1, 3, 4) and both 
becoming invested with a membrane. As the gelatinous material is excreted from the cells they 
become gradually separated from each other, the surrounding membrane is diagonally ruptured, 
and the cells are set free. The division is rapidly repeated so that the appearance is asif 4, 8, or 
16 cells originated at once from a single cell, but in the present study in no case were more than 
two cells seen to originate at one time from a parent individual. 
The shape of the cells and the formation of colonies is largely controlled by the nutrient 
medium in which the alga grows. A large number of cultures were made in different solutions, 
and it was found that 0.05 per cent Knop’s solution most nearly reproduced the species in the form 
in which it was first found. In a weak decoction of earth and in an infusion of Anabaena flos- 
aque the cells assumed a much longer and more slender form, while on agar mixed with 0.4 per 
cent Knop’s solution all resemblance to the original form was lost, the cells becoming perfectly 
spherical, with dark contents, and a wide, gelatinous envelope. In a solution containing organic 
matter from the plankton, also in the decoction of earth, gelatinous masses were formed as large 
as a pea, while in 0.05 per cent Knop’s solution the cells usually existed either singly or in smaller 
clusters of 4 to 16 cells. After some months these cultures appeared as a vivid green jelly, due to 
the great increase in the number of cells. 
In some of the general characteristics this species resembles those species of Oocystis, where 
the cells lie imbedded in a gelatinous matrix, but the fusiform shape, the greater density of the 
gelatinous envelope. and the structure of the chloroplast would all indicate that it can not be 
classified with Oocystis. 
Oocystis borgei Snow, new species. 
In frequency of appearance and the form in which it occurred this species showed great varia- 
tion during the three summers when observations were made. In 1898 it was not noted at all in 
the plankton, while in 1899 it was the most abundant of all of the Chlorophycece and appeared 
in large complexes of many cells grouped into twos, fours, or eights, and all imbedded in a homo- 
geneous, transparent, gelatinous substance. In a very few cases colonies of two cells were noted. 
In 1900 these large gelatinous masses were never observed, but the small colonies of two or four 
cells. such as described by Borge (‘00) occurred frequently. From the large’ gelatinous masses 
pure cultures were easily obtained. The cells measure 13 “4 long and 9 se broad, and the shape is 
ellipsoidal or slightly fusiform (fig. vu, 1, 2,3). 
The membrane is a thin layer enveloping the contents. Outside of this is a thick, gelatinous, 
covering which unites the cells into colonies, and varies in thickness from one-half to twice the 
diameter of the cell (fig. vu, 4,5). The membrane consists of cellulose, taking a blue color with 
iodine and sulphuric acid. Cells in the natural condition and young cells in culture showed the 
membrane to be of the same thickness at all points, but some older cells in culture, though not 
all, showed the membrane to be somewhat thickened at the ends. This thickening, however, did 
not take the nature of a wart or projection, such as has been noted in other species. The outer 
