Offspring of a Self-Pollinated Reversed Carpellate Plant of Morus alba

Abstract

In I929, the writer published the results of a breeding experiment with self-pollinated seeds obtained from a staminate plant of Morgs alba L. which had several branches showing sex reversal to femaleness (2). The progeny from these seeds consisted of pure staminate individuals, pure carpellate individuals, and individuals with mixed sex expression at the first blooming period. It was evident, therefore, that in the white mulberry an individual originally determined as a pure male had the potentialities to produce offspring of both sexes without the introduction of any new hereditary units from the outside. Sex reversal had been seen previously in carpellate plants but no trees were available at this time for experiment, although young trees were being grown in order to make a definite study of reversal to maleness in carpellate individuals. These young trees were transplanted from the greenhouse to the botanic garden, and in I932 a carpellate plant showed several small branches with reversal to maleness, developing a few staminate catkins. These branches were inclosed with some carpellate branches with cloth to keep out all foreign pollen, and a small quantity of selfed seeds was obtained. These seeds were dried for a few days and then planted in the greenhouse. The seedlings developed vigorously in a long-light photoperiod during the winter, and the next spring (I933) they were planted in rich soil in the garden. In the meantime, the spring of I934 was very dry and the original parent tree, now ten years old, bloomed abundantly and showed a decided increase in the number of reversed branches and the number of staminate catkins and flowers. Nearly all of the main branches of the tree now developed some staminate catkins. There was a decided gain in maleness in this tree since the spring of I932. In the regions of sex reversal many of the catkins were poorly developed, with part of the flowers either vestigial or distorted. In some cases ovularies were found with imperfect anthers developing in their sides.