Influence of Date of Flushing on Flowering in Pinus banksiana
NUMEROUS attempts have been made to relate the year-to-year variability in flowering of forest trees to seasonal fluctuations in weather conditions which, in turn, are believed to influence the internal physiological processes regulating flower initiation1. The pronounced effect of photoperiod on flowering, noted in many herbaceous species, appears to be lacking in forest trees, and observations indicate that most trees are photoperiodically day-neutral2,3. However, until more definitive experiments have been undertaken, photoperiod cannot be ruled out as a factor influencing flower formation.
THE DEVELOPMENTAL ANATOMY OF LONG‐BRANCH TERMINAL BUDS OF PINUS BANKSIANA
A B S T R A C T A study of the composition of long-branch terminal buds (LBTB) of Pinus banksiana Lamb. and the yearly periodicity associated with their formation, development, and elongation was undertaken. Each LBTB has lateral bud zones and zones of cataphylls lacking axillary buds. When present, staminate cone primordia differentiate from the lowest lateral buds in the lowest lateral bud zone of the LBTB. Ovulate cone primordia and lateral long-branch buds can differentiate from the upper lateral buds in any lateral bud zone. When both types of buds are present, lateral long-branch buds are uppermost. Dwarf-branch buds occur in all lateral bud zones. During spring LBTB internodes elongate, new cataphylls are initiated, dwarf branches elongate, needles form and elongate, pollen forms and is released, and ovulate cones are pollinated. During summer buds form in the axils of the newly formed cataphylls. By early fall the new LBTB are in overwintering condition and the four types of lateral buds are discernable. The cytohistological zonation of the LBTB shoot apex is similar to that of more than 20 other conifer species. Cells in shoot apices of pine are usually arranged in distinct zones: apical initials, subapical initials, central meristem, and peripheral meristem. Periclinal divisions occur in the surface cells of the apex; therefore no tunica is present. At any given time, shoot apex volume and shape vary among LBTB in various positions on a tree. In any one LBTB on a tree, shoot apex shape changes from a low dome during spring to a high dome during summer to an intermediate shape through fall and winter.
THE SEED PRODUCTION CAPACITY AND EFFICIENCY OF RED PINE CONES (PINUS RESINOSA AIT.)
The seed capacity of red pine cones varies from about 30 to over 110, depending on the size of the cone and its position in the tree crown, and is determined by the number of ovules that are structurally complete at the time of pollination. These ovules occur in a central "productive" region and constitute less than one-half of the total. The remaining ovules, most: of which are in the proximal part of the cone, never become structurally perfect, and do not contribute to seed production. Abortion of ovules in the productive region usually reduces seed production efficiency to 50–60%, and is accompanied mainly by withering of the nucellus in the first year and failure to produce archegonia early in the second year. The extent of ovule abortion during the first year varies indirectly with cone size, seed capacity, and height in tree.