Ammonia orients cell masses and speeds up aggregating cells of slime moulds

We showed some years ago that the rising cell masses of cellular slime moulds repel one another, and that this is achieved by a gas given off from the cell masses1. It is now clear that this gas is ammonia. We also have evidence that NH3 tends to speed up the movement of cells in aggregating streams which would account for its ability to repel; more NH3 on one side of a cell mass would cause a speed-up of the cells on that side, thus making the mass veer to one side.