The relation between skin resistance to gas diffusion, diffusivity and several histological characteristics of apple cvs Braeburn and Jonica was investigated. Large discrepancies were found between the skin resistance values measured by the efflux method and a diffusion method. It is believed that these discrepancies are due to the invalidity of Graham's law in tightly packed tissue, the existence of internal gas gradients and the types of tissue measured in the two methods. The differences between cultivars in diffusivity of O 2 and CO 2 in the same tissue were related to differences in intercellular space volume and cell size. The spatial pattern of the diffusivity of oxygen and carbon dioxide could be linked to the number of cells, the cell area, the cell perimeter and the internal free space volume. The considerably lower diffusivity in the skin was believed to be caused by both the skin and the very dense tissue of the outer cortex. Changes in diffusivity during storage coincided with changes in the amount of intercellular space and in the shape of the cells.

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The application of exogenous ethylene and 1-MCP simultaneously after harvest permitted restoration of the ripening process after storage in 'Conference' pears, extending the possibility of marketing and consumption.

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