hyphae, plant growth responses to ectomycorrhizal inoculation at 87 days did not relate more closely with the length of hyphae in soil (r2 = 0-50) than with the length of colonized fine root expressed as either m/pot (r2 = 077) or as a percentage (r2 = 069). Furthermore, differences in the P content and the P uptake per m of fine root of plants at 87 d (which are perhaps more direct measures of the effectiveness of ectomycorrhizal fungi in increasing P uptake) cor- related poorly with the length of hyphae in soil (r2 = 018 and 005 respectively), the length of external hyphae per m of fine root (r2 = 0 30 and 017 respectively), and the length of external hyphae per m of colonized fine root (r2 = 044 and 003 respectively) for these fungi. The ability of a Cortinarius sp. isolate (CORT. G) to increase plant growth without colonizing roots extensively could not be related to the development of hyphae in soil by this fungus.