The pollination mechanism of Abies amabilis

Abstract

The development and function of the pollination mechanism were studied in Abies amabilis (Dougl. ex Loud.) Dougl. ex J. Forbes growing in clonal seed orchards. Two adaxial ovules developed on each scale after dormancy and each ovule formed a funnel-like integument tip with a nucellus at the base of the shallow funnel. At receptivity, the seed cones were erect and the ovules inverted. No pollination drop was observed in fresh specimens but lipid microdrops were secreted on the rim and inner surface of the funnel. Water applied as spray beaded on all cone surfaces except where microdrops were present. Surfaces of the cone were observed using scanning electron microscopy to determine the presence and ultrastructure of the waxy cuticle. All surfaces that were not wettable with water were covered with epicuticular wax. Pollen did not adhere firmly to cone surfaces having epicuticular wax but adhered to the microdrops on the funnel. Drops of water picked up pollen as they moved over the waxy surfaces toward the cone axis. There, the inverted ovules were arranged in a tight helix around the cone axis. Beads of water, often containing pollen, settled on the scale surface just below the funnels and then touched and wetted the inside of the funnels, forming a column of water from the scale surface below to the funnel above. The saccate, buoyant pollen then floated up and into the funnel. Experiments were done to determine the effect of pollen application on pollen uptake into the ovule: without water, with water applied before or after pollen was applied, or as a pollen–water mix. Results support the hypothesis that A. amabilis, and likely other Abies species, lacks a conspicuous pollination drop and water as rain or dew substitutes for a pollination drop.