Postdormancy development and growth of microsporangiate and megasporangiate strobili of Abies balsamea

Postdormancy development and growth of strobili of Abies balsamea (L.) Mill, are described. Some strobilus growth occurs within the buds before bud swelling becomes detectable. The strobilus buds burst before the vegetative buds. The latter burst about 10 days after the megasporangiate buds, by which time pollen is being shed and the megasporangiate strobili are receptive. Elongation of megasporangiate strobili is divided into two stages; the first, occurring before the strobili are receptive, accompanies the grand period of bract growth; the second accompanies the grand period of ovuliferous-scale growth. The two stages are not evident when growth is expressed as dry weight. Elongation ceases in mid July, but strobilus dry weight increases until mid August. This is largely accounted for by embryo growth in the contained seeds.The moisture content of microsporangiate strobili reaches a maximum just before pollen release. Pollen grains account for about half the mature strobilus dry weight. The moisture content of megasporangiate strobili reaches a maximum at the time of fertilization, after which it declines until the strobili break up.Megasporangiate strobili situated in upper positions become larger than those situated lower in the megasporangiate-strobilus bearing zone.