Application . The period between pollen dispersal and female cone receptivity in conifer trees is very short . This constitutes an obstacle to pollination control in work done by geneticists and seed-orchard managers . However, it is possible to accelerate the male cone maturation with a localized greenhouse effect around the bud-bearing branches, produced by enveloping the male cones with paper or plastic bags .Abstract . Paper bags equipped with a polyethylene window were placed on branchlets 6 and 9 weeks before the time of pollen dispersal of Japanese larch and Jack pine, respectively . This technique produced a localized greenhouse effect around the branchlets, accelerating male cone development. For Jack pine trees, buds in bags with the window oriented upward had the shortest maturation time . In fact, it was possible to collect these pollen cones about 11 days before the unbagged control without decreasing the production of pollen . The mean germination rate of the pollen from the bags with the window pointed upward, however, was significantly lower than the control, by about 15% . Buds in bags with the window oriented downward had an accelerated development of about 9 days (compared to the control) but did not experience a decrease in pollen production or quality . This same technique caused the abortion of male cones of the Japanese larch trees . Thermal probes in the bags enabled us to follow the progression of temperature inside and outside the bags during the development of the male cone in each species . They revealed that the bags increased mean temperature, daily temperature range, and degree-day accumulation, and that this effect was most pronounced for Jack pine, when the polyethylene window was oriented upward .