REACTION ZONE PENETRATION AND PROLONGED PERSISTENCE OF XYLEM RAYS IN LONDON PLANE WOOD DEGRADED BY THE BASIDIOMYCETE INONOTUS-HISPIDUS

The white-rot basidiomycete, Inonotus hispidus, produces a characteris tic pattern of decay in naturally infected London plane (Platanus x hi spanica) in which zones of severely decayed wood, traversed by relativ ely undegraded xylem rays, alternate with relatively undegraded, gummo us 'reaction zones'. Microscopic observations of London plane wood bot h naturally colonized and artificially inoculated with I. hispidus ind icated that the resistance of reaction zones and xylem rays to degrada tion is due respectively to obstruction of cell lumina by tyloses and polyphenols, and infiltration of intercellular spaces by polyphenols. Inonotus hispidus was apparently able to circumvent these impedances b y forming soft-rot like tunnels through the wood cell walls.