377 
Physiology of the Saprolegniaceae . 
least in ordinary variable cultures. It is also to be noted, that in all the 
species of Saprolegnia which I studied from a single zoospore, and in which 
oogonia and antheridia formed at all, the antheridial filaments were of both 
androgynous and diclinal origin, or would become so under the varying con- 
ditions of culture. Whether this variability extends to all the species 
of Saprolegnia and of Achlya also, cannot be determined in the absence 
of experimental evidence. 
The results so far indicated show that it is possible to produce , where 
hitherto they were believed to be absent , antheridial branches of the normal 
type known in other species of the family , and that their production is con- 
ditioned by the presence of definite inorganic salts. It seems clear, also, that 
more radicals of salts subserve this function than was found to be the case 
in the 5. mixta studied by Klebs. At first sight, calcium might also seem 
to be necessary ; but no results were obtained with any other calcium salts 
than Ca(N0 3 ) 2 ,Ca 3 (P0 4 ) 2 ,and CaHP0 4 , and this would seem to indicate that 
nitrogen and phosphorus are the active elements. This view is strengthened 
by the fact that the most active salts are K 3 P0 4 and KN0 3 . But we have 
seen that K 2 S0 4 also belongs to the list. From the data so far at hand it 
is likely that potassium is therefore also an active element. This is also 
apparent in the cultures where K 2 S0 4 was added to the solution of Na 2 HP0 4 . 
When the latter alone was used with haemoglobin the development of 
reproductive organs was not near as definite as with K 2 S0 4 . In any case 
side-branches were produced and developed to a greater or less extent in 
all these salts when used separately with haemoglobin. 
Just what we mean when we say that one element is more active than 
another is not yet clear. Our knowledge of the process or sets of processes 
which start the mechanism of antheridial formation going is practically nil. 
We can with De Bary (’81) take the view that a chemical compound is 
excreted by the oogonia which induces the formation of antheridial filaments, 
and that the different salts offer the conditions which make the secretion of 
this active principle possible. Klebs found only the phosphates especially 
effective for the induction of antheridia ; but if it is true that nitrates and 
potassium are also active, then the problem becomes still more complicated. 
If it depends in its entirety on the improved condition of nutrition, as Klebs 
believes, then the effects of phosphates, nitrates, and potassium is more easily 
understood, although it still fails to afford any explanation of the actual 
relations of antheridial filament and mycelium. That the relations are 
chemical in nature is made plausible by the researches of Pfefifer (’84) and 
Miyoshi. It would be conceivable that some constituent of the salts used 
combines within the cell in such a way with the proteids as to set free an 
enzyme, and that this is the active principle. The origin at so many 
different points indicates that it is largely a matter of equilibrium of the 
conditions which do take part, and that the equilibrium, or perhaps lack of 
