The distribution of excitation energy in the photochemical apparatus of photosynthesis was examined with dark-grown bean leaves which had been partially greened by a series of brief xenon flashes. The yield of energy transfer from Photosystem II to Photosystem I was estimated by a method devised recently for spinach chloroplasts. Using that method, which involves a comparison of fluorescence excitation spectra with the absorption spectrum of the flashed leaves at −196 °C, the yield of energy transfer in the flashed leaves was found to be about twice the yield values obtained with chloroplasts. On further greening in continuous light, during which time the light-harvesting chlorophyll a/b protein accumulates, the yield of energy transfer decreases approaching the lower values found previously for spinach chloroplasts. The initial distribution of absorbed quanta between Photosystems I and II was also determined for the flashed leaves as a function of the wavelength of excitation. In contrast to spinach chloroplasts or to mature green leaves where that distribution is almost constant independent of wavelength at wavelengths shorter than 675 nm, the distribution of energy in the flashed leaves showed considerable variation with wavelength. The rate of photooxidation of P-700 at −196 °C was measured at two wavelengths, 645 and 670 nm, at which the initial distribution of energy between the photosystems is appreciably different. A comparison of the rates of photooxidation of P-700 with the relative intensities of Photosystem I fluorescence excited by these two wavelengths confirmed that energy was transferred from Photosystem II to Photosystem I and that the transferred energy stimulated both the photooxidation of P-700 and Photosystem I fluorescence at −196 °C.