By means of appropriate defoliation, flowering may be confined to the donor (short-day) branch and denied to the receptor (long-day) branch of a two-branched Xanthium plant during the photoinductive treatment of the donor or for any desired interval after the photoinductive treatment has been terminated. Debudding the donor, removing the mature leaves of the receptor branch, and allowing growth of the young leaves of the receptor branch all contribute to movement of the flowering stimulus from the donor branch to the receptor buds. The results of experiment I indicate that (a) the stimulus remains stable within the plant and is available to the receptor buds for considerable periods after inductive treatment of the donor has been terminated and (b) the stimulus may be stored in the young leaves and/or the buds. 2. Appropriate defoliation and debudding experiments indicate that exposure of mature leaves to short day in the absence of an actively growing bud on the plant (a) does not result in the production of the flowering stimulus or (b) the stimulus disappears shortly after it is produced and is not stored in such leaves. Young leaves, on the other hand, either store the stimulus or continue to produce it after short-day treatment is discontinued. 3. The removal of buds prior to short-day treatment renders such treatment ineffective unless young leaves are allowed to remain. The supply of the floral-initiating stimulus in periods after inductive treatment has been terminated is apparently centered in the immature tissue of young leaves and buds. This conclusion is further substantiated by the results of experiment V which suggest that the presence of buds may increase the flowering response. 4. Repeated short-day treatment of a single leaf is more effective than the division of the same number of inductive cycles between two leaves. A lapse of several days between short-day treatments lessens their total effectiveness.
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Lincoln et al. (1958) studied this question.