Developmental History of the Fruit in Lines of Cucurbita pepo Differing in Fruit Shape

Abstract

1. The inheritance of fruit shape in Cucurbita pepo may be ascribed to the operation of Mendelian factors. 2. In inbred and genetically pure lines showing the three main shapes of fruit (elongate, spherical, and disk), comparative studies were made of the developmental history of the various shape types from the earliest floral primordium to maturity. 3. From a very early stage in differentiation, when the ovary primordium is not more than one-millionth of the volume of the mature fruit, each of the various shape types is clearly distinguishable. 4. Much of the difference between the types, especially between the elongate and the spherical, was found to be due to shape differences involving only the central carpellary tissue (later the seed cavity) and not the wall of the ovary and fruit, the latter maintaining an essentially constant width in fruits of diverse shapes. 5. In most of the disk types, however, not only is the seed cavity relatively short and broad, but there is also a localized thickening of the wall in the equatorial zone (involving only the inner wall layers) which results in a still flatter shape for fruits of this type. 6. In certain lines a sterile and relatively slender neck is developed at the base of the ovary. 7. The various fruit shapes are essentially similar in the size and shape of their component cells. 8. The factors determining shape are evidently those which govern growth correlation. They operate by controlling: (1) cell polarity, and thus the plane of cell division; and (2) the localization of growth in particular regions.