. Essentials of botany. Botany; Botany. STRUCTURE OF FLORAL ORGANS 163 Fig. 120 will serve to furnish, examples of some of the shapes which pollen grains assume; c in the latter figure is perhaps as common a form as any. Each pollen grain con- sists mainly of a single cell, and is covered by a moderately thick outer wall and a thin inner one. Its contents are thickish protoplasm, full of opaque particles, and usually containing grains of starch and little drops of oil. The knobs on the outer coat, as shown in Fig. 120, 6, mark. a b c d e Fig. 120. Pollen Grains. (Very greatly magnified.) a, pu
. Essentials of botany. Botany; Botany. STRUCTURE OF FLORAL ORGANS 163 Fig. 120 will serve to furnish, examples of some of the shapes which pollen grains assume; c in the latter figure is perhaps as common a form as any. Each pollen grain con- sists mainly of a single cell, and is covered by a moderately thick outer wall and a thin inner one. Its contents are thickish protoplasm, full of opaque particles, and usually containing grains of starch and little drops of oil. The knobs on the outer coat, as shown in Fig. 120, 6, mark. a b c d e Fig. 120. Pollen Grains. (Very greatly magnified.) a, pumpkin; 6, enchanter'^s nightshade; c, Albuca; d, pink; «, hibiscus. the spots at which the inner coat of the grain is finally to burst through the outer one, pushing its way out in the form of a slender, thin-walled tube.^ 191. The Formation of Pollen Tubes This can be studied in pollen grains which have lodged on the stigma and there been subjected to the action of its moist surface. It is, however, easier to cause the artificial production of the tubes. EXPERIMENT XIX Production of Pollen Tubes. — Place a few drops of suitably diluted syrup with some fresh pollen in a concave cell ground in a microscope slide; cover with a thin glass circle ; place under a bell-glass, with a wet cloth or sponge to prevent evaporation of the syrup, and set 1 See Kerner and Oliver's Natural History of Plants, Vol. II, pp. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Bergen, Joseph Y. (Joseph Young), 1851-1917. Boston, Ginn
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