Abstract
Experiments designed to ascertain the effect of hydrogenโion concentration on encystment in Didinium were carried out by depriving didinia of food in mixtures of spring water and buffer solutions whose hydrogenโion concentrations varied from pH 5.0 to pH 9.6, and by counting the number of didinia which encysted and the number which remained active and ultimately died of starvation.
The maximum percentage of encystment was attained between pH 6.4 and 8.4, the range in hydrogenโion concentration which is also most favorable for the growth of didinia; within this range the encystment rate was practically constant and was about 52 per cent. The solutions having hydrogenโion concentrations between pH 6.4 and 5.0, the acid death limit of the race of Didinium used in the experiments, and between pH 8.4 and 9.6, the alkaline death limit, inhibited encystment, the more injurious solutions producing the greater decrease in encystment rate.
The results indicate that the limits of hydrogenโion concentration within which Didinium can live are practically the same as those found by Crane for Paramecium (approximately pH 5.0 to pH 9.6). They indicate further that concentrations of hydrogen ions which are unfavorable for the growth of didinia do not facilitate encystment and, in general, that changes in hydrogenโion concentration are of little importance in inducing encystment in Didinium.