A culture system is described to grow mycorrhizal plants which allows experimental measurements to be made on mycorrhizae, and a portion of intact ectomycorrhizal fungi while in symbiosis, but growing apart from the rooting medium and host roots. A portion of the extramatrical hyphae is kept apart from the rooting medium by a restrictive passageway between the root and fungal chambers. Fungal hyphae grow out of the root chamber onto pre-weighted glass fiber filter paper for gravimetric estimation of the hyphal mass in the fungal chamber. The pieces of the modular Root-Mycocosm can be assembled in various configurations. Ponderosa pine (pinus ponderosa Laws.) seedlings were inoculated with Hebeloma crustuliniforme Quel in either commercial-vermiculite inoculum or in plastic growth-pouches and grown in the Root-Mycocosm. Hyphae were allowed to grow into the fungal chambers and after four weeks, amounted to 5.5 + or - 0.81 SE and 6.4 + or - 1.5 SE mg for pouch and commercial inoculum techniques, respectively. (Copyright 1988 Kluwer Academic Publishers.)