4 AECD-3446(App. ) described in this study with some of those already known. Plant galls or tumors may be caused by fumgi, bacteria, viruses, nematodes, . insects, chemical substances and genetic factors. They are as varied and NURSroug as the number of inciting agents would indicate. The most intensely studied plant gall is known as Crown-Gall, whiosh is incited by Agrobacterium tumefaciens. It has been observed on plants belonging to widely separated botanical families and it has been described on almost all not organs of susceptible plents (10). The family Convolvulacene; of xhich the genus — Ipomoea, is a member is not found on this list, however. : Crown gall bacteria are=~ widely distributed and are apparently native in many soils where they lead an independent life or persist in old galls (16). It is wmoertain whether the bace teria are intercellular or intracellular, but the bacteria must be introduced through a wound; and the size of the wound determines to some extent the size of . tissue into tumor tissue. oN Apparently the bacteria produce something which transforms normal SRS Pa oF:Send the gall (9). After this, the galls can continue to grow without the inciting principle, but the nature of the inciting principle and its mode of action are unknown. Crown-gall is not a systemic disease, however, and the relative size of the tumor apparently depends on the amount of transforming prine- ciple available at the time of the cellular alteration. There is a considerable 7 histological variation in reaction to the crown-gall organism reported in the literature. es & In general, the tissues are more distorted than normal, and giant cells with many nuclei may be present (9). It has been reported by Braun (4) : that cells which have undergone the transformationinduced by the orowne-gall . organism can change back into normal cells and give rise to organs. : The host ranges of other gall-inducing bacteria are quite limited and are _ 4 not applicable to this study (27). i Inseots are probably the most common cause of galls in plants. case of a great many insects In the there is no mechanical injury, but in all cases x See x UNIVERSITY OOPS.TiP UNIV. Geov w! “ARE SS hers