Cellular slime molds in forest soils of eastern Canada

The occurrence and distribution of cellular slime molds in eastern Canada were investigated. Particular attention was given to boreal forest since there is no previous study of Acrasieae in soils of this forest formation. Four species, Dictyostelium mucoroides, D. minutum, Polysphondylium pallidum, and P. violaceum, are common in spruce–fir forest soils. Of these only D. mucoroides and D. minutum are constant and dominant. Numbers per unit of soil averaged higher than in other forest soil habitats investigated during the course of the author's researches. The relatively high densities, up to ca. 20 000/g, were limited to certain sites within a forest, probably where abundant bacteria exist, although this was not determined. Occasionally D. discoideum, D. lacteum, and Acytostelium leptosomum can also be found in the boreal forest region. Two other species, D. purpureum and D. polycephalum, were found only in deciduous forest. The distribution of Acrasieae probably extends well beyond the boreal forest proper into the hemiarctic of tundra–forest patches.