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- W623941409 abstract "collection of conifers, pollen capture generally occurs in spring. These events are subtle and unobtrusive and can scarcely compete with the simultaneous extravagance of azalea and lilac blossoms. However, with a little patience and the use of a hand lensthe viewer can observe a process that turns out to be both beautiful and mysterious. Gymnosperms, the group of seed plants to which conifers belong, are distinguished by possessing exposed (or naked) ovules at the time of pollination. The apex of the conifer ovule (the micropyle ) receives the pollen directly, usually by means of a drop of fluid ( pollination drop). Angiosperms, or flowering plants, on the other hand, retain their ovules within a closed structure (the carpel ), and the process of pollination does not involve a pollination drop. Although the pollination-drop phenomenon is easily observed, remarkably few detailed studies have ever been made of it. A large living collection of conifers, such as that of the Arnold Arboretum, offers the ideal opportunity to obtain basic information with relatively simple tools. Taxonomie Distribution of Pollination Drops Conifers that are known to produce a pollination drop include all the species that have been studied in the families Cephalotaxaceae, Cupressaceae, Taxaceae, and Taxodiaceae. In the Pinaceae, only the genera Picea and Pinus produce a pollination drop [Abies, Cedrus, Larix, Pseudotsuga , and Tsuga do not). These genera have a range of ovular morphology and pollen-engulfing mechanisms that appear to be more specialized than the pollination drop and that are therefore thought to be derived, in evolutionary terms, from the drop system. Since non-coniferous gymnosperms like the cycads, Ginkgo , and Ephedra possess a pollination drop, it is usually assumed that this general mechanism is ancestral. There is even fossil evidence for the existence of a pollination drop (Rothwell, 1977). Recently, Professor P. B. Tomlinson of Harvard University has determined that most of the Podocarpaceae in the South Pacific possess a pollination drop associated with unusual pollen-retaining features. Other Southern Hemisphere conifers, namely Agathis and Araucaria (Araucariaceae), lack pollination drops and have developed unusual mechanisms involving long pollen tubes." @default.
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- W623941409 date "1990-01-01" @default.
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- W623941409 title "Pollination drop time at the Arnold Arboretum." @default.
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