Leaf Galls

Abstract

The great dominance and complexity of galls on leaves, the association of so many diverse groups of gall organisms and numerous other peculiarities of leaf galls are related to the distinctive structural and functional characters of the leaf as organ of the plant. The high synthetic activity, rapid growth and the peculiarities of morphogenetic patterns of leaf development are other important contributory factors to the wealth of leaf galls. Cecidozoa find in the leaf a much wider choice of ecological optima (fig. 57). The conditions for development of galls on different parts of the leaf, such as for example the leaf margin, the general surface of the blade, the midrib and the larger veins, the upper side or the under side of the blade, the petiole, etc. differ within wide limits. The fact that cecidozoa may become enclosed more readily in a leaf fold or roll than in any other organ should not also be overlooked. Some of the outstanding problems in the structure, differentiation and morphogenesis of leaf galls depend largely on the fact that surface growth predominates in the leaf. Striking differences exist, however, in the cell polarities, directions of cell elongations and cell divisions between the epidermis of the upper and lower sides of the leaf blade, palisade and spongy tissues.