Responses of Seeds of Pinus taeda & P. strobus to Light.

Seeds of loblolly pine, Pinius taeda L., and of wlhite pine, P. strob!s L., which require a long moist treatment at a low temiiperature (stratificationl) for conmplete 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 (lavs at 10 C or 60 lays at 4C (27). The purpose of the work was to investigate responses of these seeds to red and far-red radiation, wvhich controls germination (4) through the phytochrome pigment (13). Phytochrome exists in two interconvertible forms (4). The P660 form absorbs re(l light and is converted to the P730 form believed to be active biologically. The P730 form absorbs far red an(l is converted to the inactive P660 form. The P7340 formn also reverts in darkness to the P630 form (13). AMost see(ls in which the action of plvtochromie has been demonstrated germinate promptly and completely after one brief exposure to light (23). A few seedls in a sample of seed of Virginia pine, P. virginiiana Mill., also germiinate in response to a single brief irradiation, but most of themii require a short period at a low temperature before they germinate in response to light (26). This change in light requiremiient of Virginia pine seeds after a short period at a low temperature made it important to measure similar changes in loblolly an(l white pine seeds, wlhich reportedly re(quire appreciable stratification.