Abstract
Smith (1911-12) in his extensive studies on crown gall and its resemblance to animal cancer shows that the physiological effects of these tumors vary from species to species and also within the species and are generally less pronounced and speedy than one might expect. He holds that it is difficult to show conclusively that the substances produced in the tumor by the parasite are absorbed and act as slow poisons. This is expecially difficult in view of the fact that the galls are often soaked by rains and become infected with other parasitic and saprophytic organisms.
Levin and Levine (1918) in a preliminary report on the malignancy of the crown gall and its analogy to human cancer pointed out that a number of the phenomena in both diseases are analogous. They contend that the neoplasms in plants produced by Bacterium tumefaciens are sometimes benign, though some are true malignant growths. The latter generally dwarf the plant so affected and cause the necrosis of the tissue above and below the gall.
These studies and those of other workers were carried out on annuals, biennials or deciduous trees in which the period of growth of the host as well as the crown gall is normally interrupted. The difficulty in determining the effects of crown gall, is made greater by the intervention of natural death, caused by changes in temperature and its concommitant factors, and second, by the occurrence of infections caused by fungi and even insect grubs, the eggs of which are deposited in the soft tissue of the young crown gall.
The purpose of this report is to bring forward further evidence on the malignancy of the crown gall experimentally induced on mature evergreen perennials such as the common rubber tree, Ficus elastica.
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