\u3cem\u3eXanthium strumarium\u3c/em\u3e L.: Extraction and Assay of Floral Promotive Principles and Additional Investigations into Inhibition of Flowering

New techniques in extraction and assay of florigenic substances were tested. Initial response to the buffer-PVP extracts proved promising, but after several successful experiments, results could not be duplicated. Possible reasons for the failure are discussed. A long-day inhibitory effect, demonstrated earlier by Gibby and Salisbury (25), was further investigated. Experiments with 14C-labled assimilates disproved the hypothesis that the inhibition is a result of assimilate translocation. Other experiments pointed to the probability of phytochrome involvement as well as protein synthesis as part of the inhibitory process. The nature of inhibition was ascribed to a localized inhibitory condition, probably a relatively immobile substance