Cytology of a new variety of A chly a americana. 143 
able thickness, and has a double contour. The inner wall is 
a mass of reserve material. This thick double wall deserves 
special attention, as it apparently has not hitherto been noted 
in Saprolegnieae. It provides one of the chief difficulties in 
the preparation of suitable sections. Figs. 19 to 23 illustrate 
fully the maturation of the oospores in the oogonium, which 
we have already had under observation during the formation 
of the oospheres. The first eggs to ripen were those nearest 
to the fertilization-tubes. They took about 5i days for the 
purpose, the weather being very cold for the time of the year. 
Germination of the oospores. The germination of the 
oospores was followed in the same oogonium. The two 
oospores nearest to the fertilization-tubes were noted six days 
after they had reached maturity to be already in course of 
germination. During this process the inner wall first becomes 
dissolved ; the protoplasm increases in quantity ; the oil- 
globule comes to occupy the central part of the spore, and 
is gradually decomposed and absorbed ; the outer wall 
stretches, and its inner layers disappear ; the oospore 
increases in size, and a vacuole is developed in the centre. 
Later, one or more germ-tubes make their appearance, and 
these as a rule soon stop growing, and produce each a small 
sporangium with from four to ten zoospores. Figs. 34, 25, and 
26 illustrate these stages in germination, and from the times 
appended it is clear that germination may be completed in 
three days. It is noteworthy that the first oospore to ger- 
minate was the first to mature, and in all probability the one 
first touched by a fertilization-tube. An intermediate stage 
in the germination of the spores is represented in Fig. 27, in 
which three oospores have produced germ-tubes. 
The foregoing observations enable us to arrange the appear- 
ances presented in serial sections either of oogonia or oospores 
in, at any rate, a rough chronological order. To anticipate 
somewhat, it may be said here that the order is sometimes 
difficult to make out. The difficulty is greatest where it 
would have been convenient for it to have been least. 
Between the stages represented by Figs. 7 and 9, representing 
