. Elements of botany. Botany; Botany. FERTILIZATION. 159 future plant is to spring. This kind of union is found to occur in many flowerless plants (Chapter XXIII), resulting in the production of a spore very unlike a seed in most re- spects, but capable of growing into a complete plant like that which produced it. 195. Number of Pollen Grains to each Ovule.— Only one pollen tube is necessary to fertilize each ovule, but so many pollen- grains are lost that plants produce many more of them than of ovules. The ratio, however, varies greatly. In the night- blooming cereus there are about 250,000
. Elements of botany. Botany; Botany. FERTILIZATION. 159 future plant is to spring. This kind of union is found to occur in many flowerless plants (Chapter XXIII), resulting in the production of a spore very unlike a seed in most re- spects, but capable of growing into a complete plant like that which produced it. 195. Number of Pollen Grains to each Ovule.— Only one pollen tube is necessary to fertilize each ovule, but so many pollen- grains are lost that plants produce many more of them than of ovules. The ratio, however, varies greatly. In the night- blooming cereus there are about 250,000 pollen- grains for 30,000 ovules, or rather more than 8 to fig. 142.—Diagrammatic Representation of Fer- 1, while in the common tilization of an Ovule. garden wistaria there are about 7,000 pollen grains to every ovule, and in Indian corn, the cone- bearing evergreens, and a multitude of other plants, many times more than 7,000 to 1. These differ- ences depend, as will be seen presently, upon the mode in which the pollen is carried from the stamens to the inner coating of ovule; w, outer coating of ovule ; p, pollen tube, proceeding from one of the pollen-grains on the stigma; c, the place where the two coats of the ovule blend. (The kind of ovule here shown is inverted, its open- ing m being at the bottom, and the stalk /ad- hering along one side of the ovule.) a to e, embryo sac, full of protoplasm ; a, so-called antipodal cells of embryo sac ; ??, central nu- cleus of the embryo sac; e, nucleated cells, one of which receives the essential contents of the pollen tube ; /, funiculus or stalk of ovule ; 771, opening into the 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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