Initiation and development of the ovulate strobilus in Pinus tabulaeformis

Thin section technique was applied in the study of the initiation and development of the ovulate strobilus in Pinus tabulaeformis Carr. In the early August, as the primordium of ovulate strobilus occurred, cytohistological zonation of cone apex was similar to those of the vegetative shoot apex, but the cone apex appeared different from the vegetative shoot apex morphologically. In mid_October, the first bract primordium was formed in the axil scale at the cone base, then bract initiation had occurred in an acropetal direction. At this phase, cytohistological zonation of the cone apex has changed into two zones, the outer mantle of small cells was derived from the apical initial zone, central mother cell zone and peripheral zone, the inner pith of larger cells originated from the activity of the rib meristem. In the middle of March, ovuliferous scale primordia were acropetally formed in the axils of the developing bracts. In the middle of April, the bract attained approximately their full size, and a pair of anatropous ovules with single integument was initiated on the adaxial surface at the base of the fertile ovuliferous scale. Ovulate strobilus continued to grow during the fall and winter, while the vegetative shoot apex entered a dormancy. No basic structural difference was observed in the vegetative and reproductive apices, but apparent difference was present in the growth characteristics.