RELATION BETWEEN VEGETATIVE VIGOR AND REPRODUCTION 545 
Achlya racemosa, this limit lies between o.i percent and 0.05 percent 
peptone. Above this limit there was an increase in the growth, 
whether the concentration of the peptone only was increased, or 
whether salts or sugar were added, but there was no corresponding 
increase in the number of oogonia produced. Results similar to those 
given in the above tables were secured from other tests and we may 
conclude that for Achlya racemosa there is a concentration of food 
which, while it will enable the fungus to make some growth, will so 
reduce its vigor as to interfere markedly with the production of spor- 
angia and of oogonia. Above this critical concentration the effect of 
the food will be marked by an increase in weight without a corre- 
sponding increase in the number of sporangia or of oogonia formed 
when the mycelium is transferred to water. For the production of the 
maximum number of sporangia this concentration lies above o.i per- 
cent peptone while for the production of oogonia it lies between this 
and 0.05 percent peptone. 
Experiments with Saprolegnia ferax (Gruith) Thuret 
This species was collected at Heidelberg in the fall of 191 1. One 
spore was isolated, and all the cultures made during the past three 
years have been with material derived from this original culture. 
This species was first clearly separated from other members of the 
"ferax group" as S. Thureti by DeBary in 1881 ('81) when he called 
attention to the fact that antheridia were scarcely ever found. Later 
('88) he distinguished 5. mixta as having antheridia on about one 
half of the oogonia and as having a more slender mycelium than that 
of S. ferax. A careful study of the form collected as number 25 failed 
to disclose antheridia and a comparison of this form with another 
collected as number 17 led to the conclusion that number 25 should be 
identified as S. ferax while number 17 had the characters of 5. mixta. 
Humphrey ('92) has discussed the nomenclature of these species and 
since his point seems well taken the name S. ferax (Gruith) Thuret is 
used here instead of S. Thureti as this species was called by DeBary. 
The fact that antheridia were found later has been recorded in a 
paper read before the Michigan Academy of Science at the meeting of 
April 1915, together with a discussion of the " ferax group " of the genus 
Saprolegnia (see Pieters, '15). 
S. ferax furnishes favorable material, since the oogonia are quite 
large and are readily produced. Klebs had already shown that 
