Pseudo-Fertility in Nicotiana

Abstract

It has long been known that the eggs of certain hermaphroditic plants and animals cannot usually be fertilized by pollen or sperms from the same individual, and this phenomenon has been termed self-sterility. Although it has been demonstrated in only one animal, Ciona intestinalis, the phenomenon has been shown to be fairly widespread throughout the plant kingdom. In 1895, Knuth listed 134 observed self-sterile species of Angiosperms belonging to 46 families, and East and Park ('17) estimated that 70 per cent of these observations proved definitely that the species were self-sterile. Hence, as early as 1895, at least 100 self-sterile species of Angiosperms had been observed. In Nicotiana, the primary difference between sterile and fertile combinations has been shown (East and Park, '18) to be the difference in rate of pollen-tube growth. In incompatible combinations, the pollen grains germinate but do not grow with sufficient rapidity to reach the ovary before the flower falls. They showed, through cytological studies of styles taken at successive twelve-hour intervals after pollination, that the pollen-tubes of fertile combinations exhibit an acceleration in their rate of growth, their growth curves when plotted being similar to those representing autocatalytic reactions. On the other hand, the pollen-tubes of sterile combinations maintain a constant rate of growth, showing no acceleration, their growth curves being straight lines. By virtue of the acceleration in the rate of growth, the pollen-tubes of compatible matings reach the ovary in less than 96 hours after pollination, whereas in incompatible matings they fail to reach the ovary within the life of the flower. 1 An investigation carried out at the Missouri Botanical Garden in the Graduate Laboratory of the Henry Shaw School of Botany of Washington University and submitted as a thesis in partial fulfillment of the requirements for the degree of master of science in the Henry Shaw School of Botany of Washington University.