In order to arrive at a better understanding of the flowering events in certain arum lilies, an effort has been made to integrate the relevant information provided by plant physiologists, naturalists, and plant biochemists with our own recent experiments. In Sauromatum guttatum Schott, the metabolic flare-up which, on the first day of flowering, occurs in the so called appendix of the inflorescence, is triggered by an agent (Van Herk’s calorigen) that arises in the male flower primordia when these are exposed to the proper régime of light and darkness. A single, 5 to 6 hour exposure to darkness of an inflorescence kept in constant light suffices to induce the flare-up, a peak in heat- and C02-production occurring about 40 to 45 hours after the beginning of the “dark shot”. Repeated exposures to darkness, at 24-hour intervals, shorten both the 40 to 45-hour lag-time and the critical length of each dark period, so that good responses occur after about 36 hrs. with a series of dark shots of 2 to 3 hours duration. The available evidence indicates that the site for perception of the second effective dark shot is in the appendix. After a single 6-hour dark shot, amputated appendices still develop heat and smell, provided the amputation is carried out at least 8 to 9 hours after the end of the dark shot. This indicates that the active principle formed in the male flower primordia as the result of the dark shot is not immediately released into the appendix. However, distribution in the appendix must be fast, since the various parts of the latter (base, middle and tip) heat up almost simultaneously, even though they do not display demonstrable differences in true lag-time, i.e., in the period between the release of the triggering compound and the peak in metabolic activity; injection of extracted calorigen into properly treated appendix-sections always leads to a peak in metabolic activity about 30 hours later. In intact inflorescences, amputation or wounding of the spathe leads to a metabolic flare-up 36 hours later. The implications of the uncovered facts are briefly discussed.