144 Troiv . — Observations on the Biology and 
a period of seven hours, the nuclei in the oogonia undergo 
a division by a typical indirect method. The study of the 
living material scarcely enables us to arrange the sections 
dealing with these dividing nuclei in exact chronological 
order. We are reduced to the necessity of falling back upon 
analogy. We have to find a complete series of forms, and then 
to determine, by analogy with better known cases of nuclear 
division, which are the earlier and which the later stages in 
the process. The condition of the oogonium in the earlier 
and later stages of nuclear division is such that there can 
be no doubt in the main as to the true sequence in which 
the facts brought to light by sections should be arranged. 
Special attention may be directed to the times necessarily 
occupied by the chief stages in the course of development. 
They are as follows : — 
From the germination of the spores to the develop- 
ment of the gametangia 4 days 
From the first appearance of the oogonial branch to 
the formation of the basal wall of the oogonium 10 hrs. 
From the formation of the basal wall of the oogonium 
to the first indication of balling 7 hrs. 
From the first indication of balling to the completion 
of egg-formation ij hrs. 
From the completion of egg-formation to the com- 
pletion of the growth of the fertilization-tubes . 1 hr. 
For the maturation of the oospores 5 days 
For the germination of the oospores, including the 
formation of the sporangia 3 days 
The whole course of development may thus be normally 
completed in a period of thirteen days. The slight differences 
of temperature in the laboratory at different periods of the 
year do not make a very appreciable alteration in the time 
required for the completion of the whole course. In July, 
in hot weather, the maturation of the oospores takes about 
five days ; in October, in cold weather, the maturation takes 
longer, but nevertheless not so much as six days. 
