375 
Physiology of the Saprolegniaceae. 
striking extent. The salts were obtained from Kahlbaum and had the C.P. 
stamp. As to the rest, the cultures were always made in series, so that the 
checks would show any outside influence. With leucin, as noted, (Ca 3 P0 4 ) 2 
and MgS0 4 also caused the appearance of antheridial side-branches, and it 
might seem from the action of so many salts that it was due to the effect of 
inorganic salts in general. To get some light as to the possible effect of 
concentration, the following was tried : Ca 3 (P0 4 ) 2 , in the concentration 
of o*i per cent., yielded antheridial side-branches very rarely in haemo- 
globin solutions. Hence a concentration half as great was used, but with 
no marked result. There is room, however, for further experimentation 
along this line. 
If we now examine the effect of the different salts in detail, we find 
that certain differences stand out in a pronounced manner. In a normal 
culture on insects or haemoglobin the usually terminal oogonium is globular, 
sometimes flask-shaped, the smooth wall rather firm and with rather large 
pits which do not project above the surface (Figs. 3 and 12). The oospores 
are from one to ten in number, sometimes more, and always centric in struc- 
ture. Attached to the base of the oogonium is the hypogynous cell, cut off 
from the rest of the oogonial filament by a cross-wall, and in length usually 
from half to once the diameter of the oogonium. Normally this cell is filled 
with protoplasm, and finger-like projections often extend from the upper end 
into the oogonium ; at times there is merely an upward bulging of the wall 
separating oogonium and hypogynous cell. 
In cultures of haemoglobin and peptone (Figs. 1, 2, and 3) the pits 
become quite prominent at times, as if the turgor of the maturing oogonium 
had pushed out the thin-walled pits. 
In calcium nitrate solutions, the cross-wall separating the hypogynous 
cell from the oogonial stalk may be entirely lacking ; when present it occa- 
sionally produces short side-branches, but these never differentiate any 
antheridia. Oogonia are formed in great abundance with a great many 
oospores, and the whole organ has a very healthy appearance, while the 
oospores matured in every oogonium during the period of examination. 
The pits vary and may be large or small. 
In calcium phosphate cultures (Figs. 8, 9, and 10). there is produced in 
the oogonial filament more than one cross-wall, at times three cells being 
cut off in this way. This was also observed in the cultures with calcium 
nitrate, as well as in some of the potassium nitrate cultures. Just what the 
stimulus is in the formation of these extra cross-walls is not very clear. 
Molisch (’95) found calcium necessary for wall-formation in Spirogyra , and 
this may also be a factor here. It is well known, on the other hand, that 
the mycelium of some Saprolegniaceae can form cross-walls under poor 
nutrient conditions, but this never occurred as far as my observations went 
in this species. Maurizio (’95) considered this doubling and tripling of cross- 
