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In the middle of the blister, on its lower surface, is a small opening, which permits the gall mites (phytoptus pyris) to pass out of the blister. The cells in the middle of the leaf are torn apart.

Blister Formed by Phytoptus Pyris by Leaf

In the middle of the blister, on its lower surface, is a small opening, which permits the gall mites…