373 
Physiology of the Saprolegniaceae . 
tions in order to find the optimum concentration for the production of 
oospores. The substances selected were haemoglobin, peptone, glycocoll, 
urea, dextrose, and fructose. The results obtained, both as to amount 
of growth under different concentrations and the time required for the 
formation of the reproductive organs of both kinds, approximate so closely 
to his results that it was decided to use his optimum concentrations for the 
further studies. 
II. 
The effect of nutrition on the development of the sexual organs was 
first effectively studied by Klebs. He also pointed out a significant varia- 
tion in the number of antheridia present under different conditions. Sapro - 
legnia mixta , studied by him, was said by De Bary to have normally about 
50 per cent, antheridia, which according to Trow are functional male organs. 
Klebs found that in a pure leucin culture — apparently o-i per cent, solution — ■ 
no antheridia appeared ; but on the addition of Knopp’s solution of inorganic 
salts, or of a mixture containing K 3 P0 4 , KN0 3 , and MgS0 4 ,the antheridia 
were formed in considerable numbers. He then tried various inorganic salts 
with o-i per cent. leucin, and found that K 3 P0 4 ,K 2 HP0 4 ,and KH 2 P0 4 caused 
the number of antheridia to be increased, potassium phosphate being the 
most effective and producing them on 50 per cent, of the oogonia. 
The form of .S', mixta used by me seems to deviate in some of these 
respects. The normal fly culture of (H) has as high as 75 per cent, an- 
theridia on its oogonia. This is also the case in a o’i per cent, leucin solution. 
It is also seen that in my cultures Ca(N0 3 ) 2 , Ca 3 (P0 4 ) 2 , and MgS0 4 acted 
so favourably on antheridial formation as to produce a yield of as high 
as 90 per cent, or even more antheridia-bearing oogonia. Not only were 
there no antheridia found in the sodium and ammonium phosphate solu- 
tions, but even the oogonia were lacking. These latter salts, then, act as 
did those in Klebs’s solutions, and inhibit in some way under the conditions 
the formation of oogonia. 
If we now compare the results obtained in S. hypogyna , the effects of 
inorganic salts in inducing antheridial growth is shown markedly. Prings- 
heim, as a result of his belief that parthenogenesis is brought about by 
changes in the external conditions, considered the plant in question as merely 
a variety of S.ferax. De Bary, however, considered it a valid species, on 
the basis of a culture which he kept for three years, and in which, he says, 
it remained constant, not only with reference to the hypogynous antheridial 
cell so characteristic of the species, but also as to the persistent absence of 
antheridial filaments. 
It was my original intention to study Saprolegnia ferax> which is said to 
lack the antheridia entirely ; whether it does so or not has to be settled by 
a culture from a single spore. As this species did not appear in my cultures 
