THE INITIATION AND EARLY DEVELOPMENT OF THE SEED CONE OF DOUGLAS FIR

Abstract

The initiation and early development of lateral vegetative, megasporangiate, and microsporangiate buds is described. The subsequent development of the megasporangiate cone prior to dormancy is described in detail. Initiation of lateral buds from cortical cells above the leaf axil occurs early in April and is similar in the three bud types. Apical zonation becomes apparent by mid-May but is less distinct in the microsporangiate primordium because of its smaller size. The microsporangiate bud remains distinctly smaller until microsporophyll initiation. Apical enlargement occurs in mid-July, at the end of the period of cataphyll initiation, and marks the onset of subsequent foliar initiation (leaves, bracts, and microsporophylls). Like the cataphylls, these foliar organs are presaged by procambial differentiation from the peripheral zone outward to the base of the presumptive primordium. No distinct apical initials appear in any of the foliar organs. A group of subapical initials is active during early development but they soon differentiate and further elongation occurs by intercalary growth. Bract initiation ends early in October. The apices of the three bud types show a similar growth periodicity and become greatly reduced in size and distinctness of zonation during foliar initiation. Scale initiation in the megasporangiate bud begins early in September and continues until the cones become dormant early in November. Scales are initiated from axillary cells at the base of the bracts. Apical zonation similar to other lateral shoots is present during early development but the organization changes to a type of submarginal growth.