Abstract
Jack pine (P. banksiana Lamb.) seeds were sown in Oct., Jan. and March, and the seedlings were cultured under accelerated growth conditions in a greenhouse. At biweekly intervals, May 15 to Aug. 15, they were transplanted to a nearby nursery and sprayed with GA4/7 or GA4/7 + NAA [naphthaleneacetic acid]. The following spring a 4-fold increase in flowering was noted in trees receiving either of the GA4/7 treatments. Trees in the March sowing did not flower. The increased flowering was caused by GA4/7-mediated differentiation of lateral long-branch primordia into ovulate strobili.