Studies in the phototaxis of Rhodospirillum rubrum. II. The relation between phototaxis and photosynthesis.

1. Simultaneous determinations were made of the saturating intensities for phototaxis and for photosynthesis of Rhodospirillum rubrum. The values of these intensities were found to be unequal in general, and their ratio was found to vary widely under different environmental conditions. 2. Some observations on the aerotaxis of Rh. rubrum are described. 3. The foregoing observations are discussed in connection with Manten's hypothesis relating phototaxis to a decrease in the rate of photosynthesis; the validity of this hypothesis is supported.