. Elements of biology; a practical text-book correlating botany, zoology, and human physiology. Biology. n A pollen grain highly magnified. It contains two nuclei {n, n') at the stage here represented. Experiment. — Germination of the Pollen Grain. Make a solution of fifteen grams of granulated sugar in one hundred cubic centimeters of water. Place on each of several glass microscopic slides a few drops of the solution and sprinkle with pollen taken from well-opened flowers of sweet pea or a nasturtium. Place on the slides some very thin and small bits of cover glass, and with these prop up th
. Elements of biology; a practical text-book correlating botany, zoology, and human physiology. Biology. n A pollen grain highly magnified. It contains two nuclei {n, n') at the stage here represented. Experiment. — Germination of the Pollen Grain. Make a solution of fifteen grams of granulated sugar in one hundred cubic centimeters of water. Place on each of several glass microscopic slides a few drops of the solution and sprinkle with pollen taken from well-opened flowers of sweet pea or a nasturtium. Place on the slides some very thin and small bits of cover glass, and with these prop up the cover slip which is placed over the sugar solution. Leave them for a few hours under a bell jar with a piece of moist sponge to keep the air in the jar moist. Examine the slides from time to time under the microscope. The grains of pollen will be found to germinate, a long threadlike mass of proto- plasm growing from it into the sugar solution. The presence of this sugar solution was sufficient to induce growth. Demonstration under Micro- scope.— Pollen tubes growing in dilute sirup. When the pollen grain germinates, one of the nuclei enters the threadlike growth (this growth is called the pollen tube; see figure). The pollen tube is therefore a long threadlike cell, which is artificially stimulated to growth bj^ the sugar solu- tion, but which in nature is brought into existence by the presence of the sweet liquid which exudes from the surface of the stigma. The cell which grows into the pollen tube is known as the sperm cell. Structure of the Pistil. — Let us now examine the structure of the pistil more in detail. (Use for this purpose any large lily.) Cut the pistil length- * Laboratory directions for other work on flowers may be found in Hunter and Valentine. Manual, paeres Three stages in the germination of the pollen grain in sugar solution. Drawn imder the compound Please note that these images are extracted from scanned page images that may
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