Morphogenesis of the leaf galls of black sage (Salvia mellifera)

The morphogenesis study of Salvia mellifera leaf galls was approached on two levels: histological examinations in the lab and growth studies in the field. Histological results revealed the galls to be neoplasms of the prosoplasmic type exhibiting determinate growth with a constancy in size and shape. Gall tissues were found differentiated into well-defined zones, however they lacked the sclerenchyma and distinctive nutritive tissues previously reported characteristic of insect galls. Histological observations revealed differences in the development of the gall's outer epidermis between galls arising on opposite sides of the leaf. This kind of comparison has been neglected in other studies. Further scrutiny found that ostiole formation involved cell separation by systematic lysis, an occurrence unusual among cecidomyid galls. Results of the field studies revealed growth inhibition in young leaves when galled. Their significantly lower growth rates and reduced biomass compared to young nongalled leaves were indicative of this occurrence. Although older galled leaves displayed a significantly lower growth rate similar to young galled leaves, their large biomass compared to young nongalled leaves indicated that older leaf growth was inhibited little, if any, by galling. No significant difference was found in growth between galls on leaves of different ages. Galls were found on nearly all areas of the leaf and on the sterns. This is the first time that S. rnellifera galls have been reported occurring on surfaces other than the leaf's undersides. No previous studies on the morphogenesis of S. rnellifera leaf galls have been done.