AbstractDaily counts were made of spores trapped on microscope slides coated with petroleum jelly and placed on the ground at distances up to 200 em from isolated colonies ofAtrichum undulatumandBryum argenteum. The observations continued for 30–34 days during the annual period of spore release in these species. Estimates of the number of spores released by the colonies were obtained as the product of the numbers of capsules and the difference between the mean numbers of spores present in undehisced capsules at the beginning of the experiment and remaining in dehisced capsules at the end.Spore deposition over the experimental periods showed a steep gradient, deposition per unit area falling from 4740—14, 230 spores cm−2in the centre of the colonies to less than 10 spores cm−2200 cm from the edge of the colonies. Despite the steep deposition gradients, however, it was estimated that more than 85% of the spores inA. undulatum, and more than 95% of those inB. argenteum, were dispersed to unknown distances beyond the trapping areas.