The intercellular system of plants is needed for gas exchange of the cells, and it forms an internal atmosphere. The investigations aimed to evaluate the intercellular system of apple fruits quantitatively and to find out possible parameters affecting it. Therefore, plastic embedded material of hypodermis, cortex, and core area was sectioned at 5 mum, stained with hematoxylin, and processed to permanent slides. The samples were investigated quantitatively using a digital image processing system for the volume percentage of the intercellular spaces. It was shown that within the fruit the intercellular volume increases from below the skin (hypodermis), reaching its maximum in the cortex and declining to the core area. The cortex, which comprises the major part of the fruit, possesses a rather uniform intercellular volume. The comparison of small and large fruits of the same variety showed positive correlations between fruit size and intercellular volume of all varieties investigated. Therefore, increasing fruit sizes result in a higher intercellular volume. higher intercellular volume compared to varieties with small fruits. The growth rate of the intercellular volume was highest in the equatorial plane of the cortex as the increase in fruit size is highest in this area. The comparison of 9 varieties showed that the intercellular volume is specific for a given variety, which is most pronounced in the hypodermis area, decreasing to the cortex and core area. A negative correlation was found between specific weight of a variety and the intercellular volume. Thus, varieties with a high specific weight have a lower gas content in their fruits and vice versa. Development of the intercellular volume during the vegetation period and storage was followed in five varieties. It was shown that the intercellular volume increases in accordance with fruit growth, forming an S-shaped curve. Within the fruit the cortex increases most intensively. During storage intercellular volume increases continuously, especially in the cortex area.
