Crossing Iris Pseudacorus and I. Versicolor

Abstract

In the progress of an experiment which was begun in the botanical garden at Grinnell College, Iowa, in the spring of i9i8, the writer attempted to produce a hybrid between Iris Pseudacorus and I. versicolor. Reciprocal crosses were made, and, as has already been reported,' the progress was most promising. When the writer left Grinnell for the summer vacation, the ovaries of the cross pollinated flowers were distinctly larger than they were at the time of pollination, were apparently still growing and appeared vigorous, while the ovaries of flowers which had been castrated, covered, and not pollinated were shriveling, had a yellowish color, and were partly separated from their stalk by an abscission layer, if they had not already fallen off. The promises of the June days were not fulfilled, however, for upon returning to the garden in early September, instead of the harvest of hybrid seeds on I. Pseudacorus that was hoped for, only a few withered pods were found still clinging to the plants. In addition to a number of wrinkled seeds, these pods yielded but one plump seed that appeared to be mature, and that one proved to be hollow. A similar attempt the following year had a similar outcome. These results raised the question as to what occurs following pollination to so stimulate growth and to prolong the life of the ovary and yet fail to produce viable seed. The investigation here reported is concerned with that problem. Both the behavior of the pollen tube and the sequence of the stages in the developing ovules have been examined. The progress of development in ovules of cross pollinated flowers has been compared with that occurring in ovules of flowers which had been self pollinated.