Date of Award
Dr. Victor Oliver
Plant galls, or cedidia, are defined as
...pathologically developed cells, tissues, or organs of plants that have risen mostly by hypertrophy and hyperplasy under the influence of parasitic organisms like bacteria, fungi, nematoda, mites, or insects.
The plant gall is unique in providing not only food, but shelter as well for its host. While the host benefits, damage to the plant results. Among other things sap flow is disturbed, premature decay results, non-essential parts are developed at the cost of essential parts, and many other injuries occur. A few examples of the benefits of plan galls may be cited. Nitrogen fixing by Bacterium radicicola on Leguminosae in root nodule galls and the cross-pollination of fig flowers by gall-forming insects are two such examples.
One theory presented is that by developing a gall around a parasite, the plant is actually defending itself. The result is that the parasite is localized and is prevented from invading other parts of the plant.
There are two basic types of plant galls. One, the organoid type galls, does not show growth abnormalities at the place where it has been attacked by the parasitic host. For example, a root parasite may cause flower deformities. These abnormalities are usually manifested in external parts of the plant. The tissues involved are normal tissues. This type of gall includes elongated or abnormally stunted internodes, bunched leaves, chloranthy of petals, etc. Parasitic fungi, mites, aphids, and occasionally Diptera and Hymenoptera are the parasitic gall makers involved in organoid galls. All classes of plants are involved.
The galls primarily dealt with in this paper are of the histoid type of gall. These differ fundamentally in their anatomy and histology from the normal organ on which they develop.
Grisham, Michael Paul, "Plant Galls" (1969). Honors Theses. 591.