The relationship between the dimensions of a spore and the accumulation of that microbe in a porous, inorganic structure has been determined. In order to achieve high accumulation of mycelial growth, at least 70% of the pores of an inorganic carrier should have pore diameters in the range of one times the smallest dimension of the fungal spore but less than about 16 times the largest dimension of that spore. This relationship was established by varying the physical parameters of the carriers as well as their chemical composition. Copyright © 1979 John Wiley & Sons, Inc.