262 LORANDE LOSS WOODRUFF 
conjugation effects ‘rejuvenation.’ In many cases encystment 
occurs and the organisms remain at the bottom when conditions 
become somewhat unfavorable; but undoubtedly the majority 
die after their period of maximum abundance. My experience 
with these cultures leaves me with the impression that conjuga- 
tion will be found to be a means resorted to by many species to 
survive acute changes in the environment, which, for example, 
preclude encystment. It is suggestive in this connection that in 
forms like the hypotrichida, which, as is well known, have a de- 
cided tendency to encyst, and the cysts of which were observed in 
great abundance at the bottom of these infusions after the active 
forms passed their maximum, not a single syzygy was observed; 
while in Paramaecium, in which the power of encystment has 
never been established, conjugation is recorded comparatively fre- 
quently. However, it is also clear from this work that a condi- 
tion which will induce conjugation in one race of Paramaecium 
will not always induce it in another, as epidemics have occurred 
between small races, while among giant races intermingled with 
them syzygies were not seen. This, of course, is in accord with 
Jennings’ studies on Paramaecium.!® The problem of the con- 
ditions inducing conjugation, and also of the effect of conjugation 
has recently become so complex from our increasing knowledge 
of the life history of various paramaecium genotypes, that the 
observations here recorded are interesting chiefly as throwing a 
side light on certain factors of the phenomenon as they appear in 
large cultures. 
IX. SUMMARY 
The following points may be emphasized: 
1. Ordinary hay added to tap water will not produce an infusion 
which is productive of a sufficient number of representative proto- 
zoan forms to make it profitable for the study of protozoan se- 
quence. 
2. Air, water, and hay are all sources from which the protozoa 
of infusions are derived, and increase in importance in the order 
19 What conditions induce conjugation in Paramaecium? Jour. Exp. Zeol., vol. 
9, no. 2, 1910. 
