Significant differences were observed in the number of bacteria present in water leachates from pots containing different plant species (wheat, subterranean clover, ryegrass), and within a plant species, during growth from seedlings to the formation of mature seed. Bactel�ial numbels in the leachates reached a peak which coincided with flowering for each plant species. The peak values for wheat, clover, and ryegrass, respectively, were 33, 77, and 99 times the number of bacteria present in leachates from control pots without plants. Subsequently, the number of bacteria in leachates from wheat pots decreased until they were not significantly different from the controls. There was a lesser decrease for the clover and no significant decrease for the ryegrass treatments.