Scanning electron micrographs showing a cross section of stalks of P. Ostreatus grown on substrates
non-supplemented (a) supplemented with gypsum (b) pumice sulfate (c) and pumice (d) after thermal
treatment. For each sample, the image was the representative image from three different samples
randomly collected from at least 10 canned mushrooms. Only mushroom caps with diameter of 7 cm and
mushroom stalks with 1 cm thickness were chosen48