294 Hazen: Lire HISTORY oF SPHAERELLA LACUSTRIS 
the size of the ordinary resting condition, and then by transferring 
them to pure water obtained megazooids through the ordinary 
mode of division. Rostafinski discovered no conjugation and con- 
cluded that Haematococcus is an asexual plant. I have frequently 
found forms presenting the appearance of two microzooids fused at 
their anterior ciliated ends but no actual meeting has been observed 
and such forms may be explained as monstrosities resulting from 
incomplete division. : 
From the conditions of their formation, however, it seems to 
me that the microzooids must be potentially gametes. Their for- 
mation does not appear to depend entirely on the conditions which 
affect the water at the time the microzooids are produced, for meg- 
azooids may be produced in the same cultures at the same time. 
On the contrary, when, from lack of nourishment or of a sufficient 
temperature, the resting-cells are unable to grow to the usual size 
and strength, microzooids are produced much more abundantly. 
I have found particularly that when. cultures containing Sphaerella 
are allowed to evaporate more rapidly than under natural condi- 
tions, the resting-cells collected on the sides of the vessel, if again 
supplied with water, nearly always produce microzooids in countless 
numbers. I have also obtained only microzooids from certain ma- 
terial collected (in Burlington) on rocks where it had been frozen 
most of the winter, but which, at milder intervals, had probably 
been able to produce small resting-cells. Material collected from 
the same place in May and June produced megazooids. 
In addition to previous conditions of growth, at the time of di- 
vision light seems to be favorable for the formation of microzooids. 
Sachs states that when a certain light intensity is reached swarm- 
spores will break forth. I have rarely been able to produce micro- 
zooids in cultures kept dark, as I have megazooids, but the same 
material, when subjected to a preparatory darkness over night and 
allowed to receive the natural gradual increase of light in the 
morning, produces abundant microzooids. On one occasion I 
found a recently motile cell in which division was beginning at nine 
o'clock in the evening ; I kept it under observation for two hours, 
during which sixteen micro-daughter-cells were formed ; but they 
did not become motile, perhaps because the light dom an ordi- 
nary student-lamp) was not sufficiently intense. 
