Bud development in Picea glauca. II. Cone differentiation and early development

Abstract

Pollen-cone and seed-cone buds of P. glauca (Moench) Voss occurred as either terminal or axillary buds. All apices initiated bud scales from late April until mid-July and then differentiated into vegetative, pollen-cone, or seed-cone apices. Potentially pollen-cone apices were usually smaller, had a lower mitotic frequency, and initiated fewer bud scales than potentially vegetative or seed-cone apices. In late July a marked increase in mitotic frequency occurred in differentiating reproductive apices resulting in changes in apical size, shape and zonation. Leaf, bract and microsporophyll initiation began at the end of July. All microsporophylls were initiated by early Oct. when pollen-cone buds became dormant. Sporogenous cells had differentiated but meiosis had not begun. Bract initiation began in early Aug. and ovuliferous scale initiation began in late August. Initiation of both stopped in mid-Oct. when seed-cone buds became dormant. Megaspore mother cells were present in dormant seed-cone buds but had not begun meiosis. There was no difference in the time of vegetative, pollen-cone, or seed-cone bud differentiation at the 4 locations from which collections were made in 1975 and 1976. Differentiation coincided with the end of lateral shoot elongation which was during the last half of July. These results agree with another report from one location in Ontario [Canada]. Temperature sums also could be an accurate method of determining the time of cone-bud differentiation if calculations were based on the end of vegetative bud dormancy rather than on more arbitrary starting dates. The methods may be applicable to other members of the Pinaceae to determine the optimal time for cone induction treatments.