The behaviour of pollen tubes and the developmental process of ovules in Pelargonium

Summary The ovary of Pelargonium species is composed of 5 carpels, each of which contains 2 ovules. Usually, one of the two ovules develops and the other shrivels. The developed ovule is either on the upper side or on the lower side in the carpel. Intervarietal or interspecific difference was observed with respect to the position of the developed ovules. In order to determine the mechanism of fertilization, the behaviour of pollen tubes was observed under the fluorescence microscope and the developmental process of ovules was anatomically examined by using two cultivars, Bourbon 4x (2n=154) and Prince Rupert (2n=22). In both cultivars, many pollen grains germinated on the stigmas, but pollen tubes which reached ovaries were few. Eventually only one tube could enter the ovule in each carpel. In Bourbon 4x the ovules which were penetrated by the pollen tubes were always the upper ones. In Prince Rupert about 70% of the total fertilized ovules were on the upper side. The dying off of embryos occurred rarely. It is concluded that the intervarietal difference in the rate of the upper ovules which develop is genetical and is determined by fertilization.