Effects of β-cedrene and α-humulene on the formation of an ectomycorrhizal (ECM) symbiosis between Pinus massoniana and Suillus bovinus. Morphology of dichotomous root branches of seedlings subjected to: a S. bovinus inoculation (M), b M+β-cedrene; c M+α-humulene treatment; or d no inoculation (NM). Cross-sections showing the microstructure of the P. massoniana–S. bovinus ECM association of seedlings subjected to: e M; f M+β-cedrene; g M+α-humulene; or h NM; the dye used was 0.03% trypan blue. i Depth of Hartig nets and j thickness of mantle under different treatments. Error bars indicate ± the SE, n = 5. Different letters above bars indicate significant differences between treatments. Red arrows indicate extraradical mycelium, white arrows indicate the mantle, and yellow arrows indicate Hartig nets.