Vegetative Mycelium of Saprolegma. 
7 i 
Time. 
12 noon 
4 p.m. 
4.30 p.m. 
10 p.m. to 3 a.m. 
5 a.m. 
6 a.m. 
6.30 to 7 a.m. 
7 to 11 a.m. 
11 a.m. to 12 noon. 
. Zoosporangium. 
Spores germinate. 
Septum growing upward. 
Ditto. 
Septum still growing, nuclei lower 
in the hypha divide, to be 
carried upward for the next 
sporangium on the next day. 
Old sporangium filled by out-\ 
growth of septum. 
Cytoplasm ceases to flow into 
new sporangium. 
Septum formed and cytoplasmic 
continuity broken. 
Zoospore origins formed and 
zoospores round off. 
Zoospores escape. ' 
Zoospore. 
Liberated. 
Second motile stage. 
Reaches host and germinates. 
Movement of cytoplasm rapid, 
germination advancing, nuclei 
divide sufficiently to serve the 
hypha next day. 
Germ-tube lengthens, branches 
formed, no more nuclear divi¬ 
sions. 
The vegetative nuclei can be stimulated to division at any time of day. 
A culture is placed in a very cold greenhouse for two days, where the water 
can be kept at about 4 0 C. The flies are then suddenly removed to water 
at 22° C., and are left at that temperature, which is a little above the 
optimum, for from ten to twenty minutes. The material is then fixed with 
hot acetic Merkel’s solution. Nuclear figures can usually be produced in 
this way ; they are always amitotic. 
Discussion. 
Hartog and Trow, who have both studied the nuclei of the vegetative 
hyphae of Saprolegnia , disagree on the method of division. The latter 
states that a direct division takes place in the zoospore, but in his figures 
this is not well shown. Hartog describes a rudimentary mitosis which 
he calls a transition between a direct and an indirect division. He saw four 
small granular chromosomes, which split longitudinally and then separated, 
no spindles being present. His figures are not distinct, and it is difficult to 
see how he could have observed such small granules splitting longitudinally 
without staining them ; in only one or two figures is it possible to distin¬ 
guish the four chromosomes. No similar figures were seen during this 
investigation. 
If the division is by the indirect method, the chromatin granules 
should have a part in chromosome formation. Here, however, the mem¬ 
brane remains intact during the division of the chromoblast, and only 
separates in the last stages when the chromatin has divided. The fact that 
the linin threads remain attached to the chromoblast throughout the 
