Seeds of loblolly pine, Pinus taeda L., and of white pine, P. strobtus L., which require a long moist treatment at a low temperature (stratification) for complete germination, were chosen for this study. Seeds of the former species require 30 to 90 days at 2 to 3 C and those of the latter 30 days at 10 C or 60 days at 4 C (27). The purpose of the work was to investigate responses of these seeds to red and far-red radiation, which controls germination (4) through the phytochrome pigment (13). Phytochrome exists in two interconvertible forms (4). The P660 form absorbs red light and is converted to the P730 form believed to be active biologically. The P730 form absorbs far red and is converted to the inactive P660 form. The P730 form also reverts in darkness to the P660 form (13). Most seeds in which the action of phvtochrome has been demonstrated germinate promptly and completely after one brief exposure to light (23). A few seeds in a sample of seed of Virginia pine, P. virginiana Mill., also germinate in response to a single brief irradiation, but most of them require a short period at a low temperature before they germinate in response to light (26). This change in light requirement of Virginia pine seeds after a short period at a low temperature made it important to measure similar changes in loblolly and white pine seeds, which reportedly require appreciable stratification.