Structural Resistances to Mass Transfer in the Lichen Xanthoria Parietina

SUMMARY Quantitative morphological data obtained from Xanthoria parietina by light and electron microscopy is related to measurements of photosynthesis rate and estimates of biotrophic ribitol transfer. It is concluded (a) that diffusive CO 2 flux into the alga is greatly reduced by the resistance of the fungal cortex, (b) that diffusion can easily account for the mass transfer of ribitol from alga to fungus, and (c) that haustoria have no role in the biotrophic transfer of carbohydrate in lichens.