Translations:Manfred Klett: Von der Agrartechnologie zur Landbaukunst/1380/en

hormonal action causes the two-dimensionality of the oak leaf to grow out from the point of oviposition into a gall, that is, into three-dimensionality. In the gall, which houses the larva, the leaf develops into a kind of spherical, skin-like organ, an interior rich in nutritive tissue that seals itself off from the outside. Gall formations also occur on other woody plants. The oak, however, as a single host plant, is capable of producing over 100 different types of galls. Remarkable is the high content of tannic acids and dyes in the galls, which again indicates a premature sulfurisation in the leaf region, similar to that in the rind and bark.