SYNOPSIS. Eighteen strains of algae, including 17 exsymbiotic from Paramecium bursaria, were tested for infectivity for P. bursaria, syngen 2 aposymbiotes, and Concanavalin A (Con A) agglutinability. All 6 infective algal strains were relatively resistant to agglutination by Con A, suggesting that algal surface characteristics are correlated with infectivity. Among the noninfective strains, high and low agglutinability were about equally represented, indicating that the Con A titer alone is not a sufficient indicator of infectivity. It is suggested that noninfective algal strains are the progeny of mutations occurring within the endozoic population and fortuitously selected by the external culture medium.

SYNOPSIS The effect of exposure period and concentration of algae on the frequency of infection of aposymbiotic ciliates by algae obtained from the same clone of Paramecium bursaria syngen 2, was studied. The frequency of infection was roughly proportional to the algal concentration and to the exposure time of ciliates to algae. The relationship of algal concentration to infection frequency closely fitted the Poisson distribution curve for N = 1, suggesting that the minimum number of algae required to infect a single ciliate is 1. However, the data also strongly suggested that the average number of algae required to initiate infection of an average ciliate was ˜ 1,000. Three possible resolutions of this situation are: (a) the selection by the ciliate of a rare infective variant from a heterogeneous population: (b) the rare escape of an alga from digestion by the ciliate; and (c) the requirement for a large number of algae‐ciliate contacts to induce susceptibility in the ciliate. Splitting the exposure of ciliates to algae into 2 periods of 0.5 h, separated by 5 h in the absence of algae, produced a much higher frequency of infection than a single l‐h exposure, supporting the suggestion that the large number of algae is required to induce susceptibility in the ciliate which can then be infected by as few as a single algal cell.

and c1 would be an underestimate of p, at least during the early stages of equilibration lag. If the vessels were paired for oxygen (1) then a = a' and cl = pl { a K,/Kl -k2/k1 } If, however, there was a big enough burst of CO2 during this period then c1 could exceed 3,k. That is there could be an apparent burst of oxygen.Sufficient has been said to show that estimates of rates of gas production from manometer readings over a relatively short period, subsequent to a change of conditions which result in a change in rate, can be misleading. LITERATURE CITED

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Studies on the influence of light on respiration have yielded different results with different organisms. In some instances results were interpreted as evidence for light stimulation of respiration (3,4,5,6), in other cases for photoinhibition (8,13), and in still other examples for a negligible effect (1). With a given species simultaneous measurements of respiratory and photosynthetic 02 metabolism have shown that the influence of light on respiratory processes varied with experimental conditions (3,4