ABSTRACT
In addition to the work on flower initiation, Xanthium has been used in several other projects. This chapter is a revision of the author’s review on Xanthium published in 1969. In addition to the taxonomic and ecological implications of C. McMillan’s work, his papers make it clear that there is a great deal of variation in photoperiodic response among the various complexes of Xanthium. Xanthium is a monoecious plant with staminate terminal inflorescences and pistillat axillary inflorescences. When a plant is induced to flower, axillary buds typically grow into branches, each with a terminal staminate inflorescence and axillary pistillate flowers. It has become increasingly apparent that spectral dependence in the flowering of Xanthium is strongly influenced by the time during the experiment when irradiations are given. Although this relates to the problem of time measurement, the chapter reviews the basic facts.
