Cytology of a new variety of A chly a americana. 139 
young oospores, it suffices to take a five-day culture and 
plunge it instantly into the fixing fluid. 
So many changes take place during the development of 
the gametangia and gametes, and the maturation and ger- 
mination of the oospores, that they need to be followed closely 
by direct observation of the living material under the micro- 
scope. The different stages are easily recognized, and their 
true sequence may be determined to a very great extent by 
observation and comparison. The determination of the 
actual sequence, however, and especially of the time involved 
during the complicated procession of events which lead up 
to the formation of oospheres, necessitated a resort to the 
method of continuous observation. A considerable amount 
of time was spent on this study, but the record of two 
observations will suffice to put us in possession of the funda- 
mental facts. 
Development of the gametangia and oospheres. A moist 
chamber culture was examined at 9 a.m. on October 7, and 
a hypha bearing three short branches selected for observation. 
These branches remained unchanged until noon, when they 
began to swell at their apices. Fig. 2 represents their condi- 
tion at 12.30. The absence of a vacuole should be noted. 
The young oogonium marked b was selected for further study. 
At 2 p.m. the oogonium was nearly full grown ; at 3.20 p.m. 
the antheridial branch began to develop, its place of origin 
being recognizable as early as 2.0 p.m. The antheridial 
branch came in contact with the base of the oogonium at 
3.45 p.m. The antheridium was cut off by the appearance 
of a transverse wall at 6.10 p.m., and the basal wall of the 
oogonium appeared at 7.25 p.m. It appears to be the rule 
for the oogonium to be segmented off after the antheridium. 
The basal wall makes its appearance very suddenly as a thick 
membrane, separated by a narrow clear space filled with 
hyaloplasm from the dense granular peripheral protoplasm 
of the oogonium. The course of development is represented 
in Figs. 3-7. From 2 p.m. to 7 p.m. the vacuole in the 
oogonium suffered many changes. At first it was small, 
