. Botany for agricultural students . Botany. POLYEMBRYON'^" 467 from the embryos of Dicotyledons in the relative positions of the cotyledon and plumule. Although the cotyledon apparently arises laterally, it soon becomes terminal and the plumule appears to develop on the side of the em- bryo (Fig. 413). Parthenogenesis. — Partheno- genesis, which is the develop- ment of an embryo from a sup- posedly unfertilized egg, occurs in a number of Angiosperms. In the Dandelion (Taraxacum), Meadow Rue (Thalidrum), Ever- lasting (A ntennaria), Apples, Pears, Quinces, and a few other plants parthenog
. Botany for agricultural students . Botany. POLYEMBRYON'^" 467 from the embryos of Dicotyledons in the relative positions of the cotyledon and plumule. Although the cotyledon apparently arises laterally, it soon becomes terminal and the plumule appears to develop on the side of the em- bryo (Fig. 413). Parthenogenesis. — Partheno- genesis, which is the develop- ment of an embryo from a sup- posedly unfertilized egg, occurs in a number of Angiosperms. In the Dandelion (Taraxacum), Meadow Rue (Thalidrum), Ever- lasting (A ntennaria), Apples, Pears, Quinces, and a few other plants parthenogenesis is known to occur. In cases which have been investigated cytologically, it has been found that the mother cell in the ovule omits the reduc- tion division, and, therefore, the cell which occupies the position of an egg has the sporophytic num- ber of chromosomes and fertiliza- tion is not necessary. Since par- thenogenetic plants show no re- sults of crossing in the offspring when cross-pollinated, partheno- genesis may be a source of disap- pointment to the plant breeder. Parthenocarpy. — Parthenocarpy is the development of fruit without fertilization and is quite common among Angiosperms. Bananas, seedless Oranges, and seedless Currants are familiar examples of parthenocarpic plants. Sometimes Apples develop without seeds, and some varieties of Cucumbers develop fruits without pollination. Polyembryony. — In a few Angiosperms, of which one of the Onions [Allium) is a notable example, a number of embryos may be developed in the same embryo sac or around it. The syner- gids and antipodals have been known to develop embryos, and sometimes some of the cells of the nucellus around the embryo. Fig. 413. — A monocotyledon- ous embryo as typified by that of Corn. The cotyledon (c) appears terminal and the plumule (p) as arising from the side of the em- Please note that these images are extracted from scanned page images that may have been digitally enhanced for
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectbotany, bookyear1919
