686 McAllister . — Nuclear Division in Tetraspora lubrica . 
species given by Collins (8) overlap in regard to the size of the cells, — the 
specific characters being based to quite an extent upon the form of the 
thallus. 
Colonies brought into the laboratory during afternoons in July and 
August and kept in small glass dishes were quite sure to form abundant 
zoospores upon the following morning. If the morning were cloudy the 
period of maximum zoospore formation might be as late as eleven o’clock. 
During the afternoon they were produced in much smaller numbers. Often 
a second crop is produced the second morning and some may even be 
formed on the third and fourth days. 
In many instances, on the second and third mornings after the fresh 
material has been brought in, the cells in certain areas of the thallus are 
seen to be in active division. Eight cells are usually formed from one 
vegetative cell, — though at times but four are formed. These latter cases 
are probably from the smaller vegetative cells. This cell division goes 
on rapidly, and in a short time much of the gelatinous thallus has dis- 
integrated. 
The new cells formed by this rapid division become biciliated and soon 
swim away. Later they may be seen in various stages of fusion in pairs. I 
found no evidence, however, of their retaining their motility after fusion. 
Neither was there evidence of the formation of thick- walled resting spores. 
During this period of rapid nuclear and cell division, leading up to the 
formation of gametes, many mitotic figures are easily obtained. 
The chlorophyll of the cells of Tetraspora occupies a cup-shaped area 
at one side of the spherical cell. A relatively large flattened pyrenoid lies 
in the thickened base of the cup (PL LVI, Fig. i). This distribution of the 
chlorophyll can easily be determined in living cells, but in material fixed in 
Flemming’s or Merkel’s fixative and stained in Flemming’s triple stain or in 
Heidenhain’s iron haematoxylin stain, no difference can be observed in the 
texture or staining reaction of the protoplasm of the chlorophyll-bearing 
area and that of the protoplasm surrounding the resting nucleus. 
The resting nucleus of Tetraspora conforms in its general details of 
structure with the better known nuclei of the vascular plants. By suitable 
staining with Flemming’s triple stain or with Heidenhain’s iron-alum 
haematoxylin, a very delicate reticulum with numerous net knots can in 
all cases be demonstrated (Pigs. 2, 3 and 26). The reticulum is so delicate, 
however, in these minute nuclei that with careless staining it may not be 
visible at all. In such instances the nucleole seems to lie in a clear area 
which usually shows no evidence even of a nuclear membrane. I have had 
a similar experience in staining the nuclei of Ulothrix zonata. These results 
are suggestive and may indicate that in those cases in which the nuclei 
of Fungi and Algae which are cited as lacking a reticulum and having all the 
chromatin collected in the nucleole, — the staining has been at fault. This 
