EVIDENCE FOR A SWARMING SUBSTANCE WHICH STIMULATES COLONY FORMATION IN THE DEVELOPMENT OF PEDIASTRUM DUPLEX MEYEN

¹ Department of Biology, Princeton University, Princeton, New Jersey

1. The characteristics of growth and reproduction in P. duplex Meyen have been studied in non-bacteria-free cultures using large inocula of 5 cc. of stock culture for every 50 cc. of fresh medium.

2. It has been found that colonies grown under these conditions exhibit two phases of development: A latent period in which no colony production or swarming takes place but during which the colonies grow, and a period of active swarming or burst phase during which all the cells of the starting colonies give rise to new colonies.

3. It has also been shown that a heat-stable substance is present in aged medium which can, through an effect other than pH, alter the time at which colony production begins, the number of colonies produced and the size of these colonies in terms of cell numbers.

4. It is suggested that the length of the latent period of development is determined by the time required for this substance to reach a threshold concentration. The possible importance of such a substance to free-living forms of Pediastrum in nature is also discussed.