In a previous investigation (1) on the malignancy of the crown-gall and its analogy to animal cancer, the writers have demonstrated that a crown gall does not develop through the specific neoplastic properties of the Bacterium tumefaciens. The mechanism of the formation of these tumor-like structures takes place in the following manner: The invasion of a plant or its inoculation by Bacterium tumefaciens is followed by an attempt of the host at self protection. Since a plant organism lacks blood, lymph, and lymphoid tissue, this protective mechanism cannot attain the character of an inflammatory process with subsequent scar formation. Therefore, in plants this protective mechanism must be supplied by the life functions of all the tissue cells in the neighborhood of the invasion of the parasite. That this life function of the tissue cells would consist in their active proliferation and in the undifferentiation of the newly created young cells is a priori more than plausible. Evidence was brought forward in the previous investigation to support this view.

In the present publication further studies are reported on the mechanism of the formation of neoplasia in plants subsequent to their invasion by parasites.

A striking instance of undifferentiation of newly formed cells for purposes of self-protection is presented by the junior writer (2) in his study on the mechanism of the formation of the leafy crown gall, in which he adduced evidence to show that Bacterium tumefaciens does not cause the formation of leafy shoots in Bryophyllum calicynum but rather inhibits and retards their normal development, when inoculated into the totipotent cells which appear at the notches of the leaf. The following is in brief the method of investigation employed: When leaves of Bryophyllum are detached from the mother plant and put on moist soil, the marginal notches of the leaves at which totipotent cells are found develop into leafy shoots and eventually form new plants. In this study the junior writer inoculated notches of one side of the leaf, by pricking the tissue five to ten times with a delicate needle containing a culture of Bacterium tumefaciens. The inoculated notches of the opposite side of the leaf served as controls, after they had been pricked with a sterile needle. As a result of the experiment the notches infected with Bacterium tumefaciens in the great majority of cases, instead of developing leafy shoots formed ordinary crown galls (figure 1, A), while the control notches pricked with a sterile needle all developed leafy shoots (figure 1, B). Occasionally a poorly developed shoot appears over a gall.

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