The Abnormal Flower and Fruit of May-Flowering Dwarf Cavendish Bananas

Abstract

1. Fruits of the Dwarf Cavendish banana which are abnormal in shape occur in Israel and elsewhere as the co-called May-shooting bunches ("November bunches" in Australia). Certain external characteristics of these bunches have been previously reported: a lesser number of hands in the bunch and thickened fruit, a decreased number of stamens, and a swelling at the top of mature female flowers or of the fruits. 2. The structure of normal female and male flowers is given as a basis for comparison of structure in the abnormal flowers. 3. In all May bunches there was a large percentage of flowers with less than the normal five stamens. This decrease was found to be the result of the adnation of stamens to the style and the arrested development of some of the stamens which remained dwarf and staminodal. 4. In many flowers of the May-shooting bunches abnormal swellings of different sizes were present at the base of the style. These resulted from the adnation of stamens to the style, the development of nectariferous tissue between the stylar sectors (ridges), and the development of a starchy parenchyma similar to that of the fruit. In addition, ovary locules which often contained ovules were found in large swellings. The arrangement and number of locules and structure of nectary were similar in the swelling and the ovary proper. In many instances a yellowish-white mass of nectariferous tissue, which turns brownish-black, was found on the external surface of the basal part of the style; it contained typical epithelial cells. 5. The number of locules in the ovaries of abnormal flowers and fruit was lower than normal in many cases: instead of three, two, one, or even no locules at all occurred. Nectariferous tissue occupied the region of the missing locules and, in extreme cases where there were no locules at all, the nectary filled the entire ovary as in male flowers. 6. The ratio of nectary length to ovary length was higher in abnormal than in normal flowers. 7. The decrease in number of locules results in many fruit not reaching normal size, so that in mature hands small and normally sized fruit are found side by side. 8. The youngest ontogenetic stage at which modifications from the normal could be detected occurred in flowers whose total length was 5 mm.