Mycorrhizal synthesis studies revealed that allopatric populations of Suillus granulatus differ in host specificity. Tissue cultures of Suillus granulatus used were from Nepal, (associated with Pinus wallichiana), Korea (Pinus densiflora) and the U.S. (Pinus strobus). Mycorrhizal effectiveness was used to measure host specificity. Useful characters for measuring mycorrhizal effectiveness were determined by ANOVAs between the uninoculated controls and mycorrhizal treatments. In addition, those characters which were stable within one population were determined via ANOVA. Useful characters, as defined by these two tests were: shoot wet weight, total wet weight, percentage mycorrhizal short roots, shoot dry weight, total dry weight and Hartig net penetration. These characters were subsequently used to measure variation in mycorrhizal effectiveness among the allopatric populations of Suillus granulatus. Isolates associated with Pinus strobus were most effective with Pinus strobus and least effective with the other trees, whereas isolates from Pinus wallichiana and Pinus densiflora showed variable effectiveness with all three trees. Phenetic analyses used to determine how similarly the isolates responded with the hosts confirmed these results. We conclude that isolates associated with Pinus strobus are most specific for this host, whereas isolates from the other two trees are not host specific. These results are discussed and hypotheses put forward to explain them. / Master of Science