The relationship between time of pollination, pollination efficiency, and cone size in western red cedar (Thuja plicata)

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Abstract
The pollination mechanism in western red cedar (Thuja plicata Donn) is described for container-grown clones. The seed cones ended dormancy at the end of February 1986, opened exposing the ovules, and soon after secreted pollination drops. Unpollinated cones remained open and secreted pollination drops for 15 to 20 days, before the expansion of the bract scales completely covered the ovules. The presence of pollen hastened cone closure so that it occurred within 4 or 5 days of pollination. Pollen in the micropyle was essential for ovule maturation and subsequent cone development. The developmental stage of the seed cones at pollination influenced the proportion of ovules per cone containing pollen (pollination efficiency). Each cone bore between 13 and 16 ovules. The proportion of ovules per cone that received pollen in the micropyles was highest when pollinations were conducted after cone opening but before bract scale expansion. A positive relationship was found between pollination efficiency and the length of mature seed cones.