Bristol.— Life-history and Cytology of Chlorochytrium grande. 109 
rain-water. The cells gradually increased in size, the cell-wall thickened, 
and zoogonidangia were formed which entered into a resting condition. 
3. In the weaker mineral salt-solution the effects were almost identical 
with those in the stronger solution, but the cell-walls were less thick. 
4. Cultures in distilled water were prepared from the original material 
and also from material which had been in rain-water or in the strong mineral 
salt-solution for some weeks. In every case the most noticeable feature of 
the cells after they had been in distilled water for a few weeks was the 
enormously thickened cell-wall (Text-fig. 1, e). Multiplication by aplano- 
spores did not take place at all, and on one occasion only was reproduction 
by zoogonidia observed. In this case a quantity of material which had been 
transferred from the strong mineral salt-solution to distilled water was 
placed upon a slide for examination. It was kept on the slide under 
observation for a fortnight, being kept moist with distilled water, and at the 
end of that time the zoogonidia were produced. 
The cells do not seem able to withstand drought. Owing to constant 
evaporation of the water in which the material was kept, a certain amount 
of the alga was left stranded on the sides of the bottle in the form of a green 
scum. The cells under these conditions retained their green colour, and 
except for a slight shrinkage of the cytoplasm presented the same appear- 
ance as normal cells. Three cultures were prepared from this material, in 
rain-water and the two mineral salt-solutions respectively, in order to find 
out whether the cells had retained their vitality. No multiplication took 
place in either of the three cultures, and the cells soon lost their green 
colour and became disintegrated. 
The Vegetative Cell. 
Vegetative cells of this alga are spherical or subspherical in shape, but 
may be ellipsoid (PI. V, Figs. 1-3) ; they vary considerably in size. Average- 
sized spherical and subspherical cells measure from 65-70 /x in diameter, 
while ellipsoid cells may be 65-75 /x long and 55-65 /x broad. Occasionally 
very much larger individuals can be found measuring even as much as 
104 /x long and 97 *x broad, but this is exceptional. 
The Cell-Wall. 
The wall of the vegetative cell is usually thin, and in spherical cells is 
of uniform thickness throughout, while in ellipsoid cells a slight thickening 
is sometimes noticeable at the narrow ends. Faint concentric striations 
in the cell- wall indicate that its composition is not homogeneous. When 
treated with iodine the wall acquires a deep reddish-brown colour ; on the 
addition of concentrated sulphuric acid to the preparation, the outer layers 
of the wall remain unchanged, while the inner layers gradually darken until 
