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Fluorescence Digital Image Gallery

Pine Tree Pollen

Pine is the common name for any species belonging to the genus Pinus, a member of the family Pinaceae, coniferous trees with needle-like leaves. Pinaceae is the largest family of conifers, consisting of about 262 species, and includes fir, larch, spruce, hemlock, and cedar.

Pine trees are gymnosperms, non-flowering plants that produce exposed seeds not enclosed in an ovary. They are monoecious, bearing gametes of both sexes on the same tree. These gametes are housed in a structure called a strobilus, or cone. Female pine cones are generally found in the upper branches of the tree crown, above the male cone. This reduces the possibility of self-fertilization by the wind-borne male gametes.

The male pinecone, or microstrobilus, produces the pollen, or male gametes. The cones are covered with fertile scales (modified leaves), each of which bears two pollen sacs. In the spring or early summer, the pollen sacs release their pollen grains, each of which has two air bladders for wind dispersal. During pollination, the pollen grains sift among the scales of the female cone and land directly on the ovules, or unfertilized seeds. Over a two to three year period after fertilization, the woody female pinecone develops. In some species, the cones open at maturity and the seeds are released. In others the cones remain closed for several years until opened by rotting, by food-seeking animals, or by fire. In some pines the scale bearing the nutlike seed may be expanded to form a wing for airborne dispersal.

Some pine trees produce seeds known as pine nuts (pignons, piñons, pignoli) that are popular in human cuisine. Although most nuts are technically fruits, pine nuts are not because they are not formed by a flowering plant. Piñons from pines in the western United States have historically been an important food source for Native Americans. The stone pine (Pinus pinea) in Italy has been prized since ancient Rome for its pignoli, which are still used for food.

Pine trees are found worldwide, primarily in northern temperate regions. Typically they have woody stems covered in bark, which protects tissues that conduct nutrients and water. When harvested, they provide materials like lumber, turpentine, rosin, paper, pulp, fuel, and even food (pine nuts).

The specimen presented here was imaged with a Nikon Eclipse E600 microscope operating with fluorite and/or apochromatic objectives and vertical illuminator equipped with a mercury arc lamp. Specimens were illuminated through Nikon dichromatic filter blocks containing interference filters and a dichroic mirror and imaged with standard epi-fluorescence techniques. Specific filters for the stained pine cone thin section were a B-2E/C and a Y-2E/C. Photomicrographs were captured with an Optronics MagnaFire digital camera system coupled to the microscope with a lens-free C-mount adapter.

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