Histological Comparison of Cucumber Fruits Developing Parthenocarpically and Following Pollination

Abstract

1. The development of cucumber fruits of a naturally parthenocarpic variety (Rollison's Telegraph) was studied before and following pollination. The development of megagametophyte, embryo, and seed coats was observed in detail. Tissues of the perianth, stigma, nectary, and neck shriveled within a week after pollination, and a protective periderm formed at the apex of the live tissue beneath. Twenty days after full bloom hardened seed coats contained large well-developed embryos. 2. Development of untreated fruits in which there was no pollination was essentially the same, except for the absence of embryos and endosperm, the disintegration of megagametophytes, and the slightly smaller size of the seed coats. 3. In other cases transverse cuts were made through the lower portion of the floral tube and a 2 per cent mixture of indoleacetic acid in lanolin was applied to the cut surface. 4. When application of the mixture was made 4 days before full bloom, apical tumors were formed, involving tissues of the nectary, floral tube, and neck. These reached maximum size in about 12 days. Neither vascular tissues nor root primordia were differentiated in the tissues of the tumors. Ovules developed to about half normal size, and seed coats became partially hardened. 5. When pure lanolin was applied 4 days before full bloom, death of the apical tissue was greatly retarded and usually no periderm was formed. Ovules developed as in untreated controls. 6. When indoleacetic acid in lanolin was applied at full bloom the apical tissues remained alive but proliferated very little. Ovules were intermediate in size between those of controls and those of fruits given the pre-bloom treatments with indoleacetic acid in lanolin. 7. When pure lanolin was applied at full bloom, development was essentially the same as that of untreated controls. 8. In the unfertilized ovules of parthenocarpic fruits the nucellus generally developed into a massive tissue with a large central cavity. 9. Meiosis and megagametophyte development were not noticeably affected by any of the treatments. 10. In a single instance following premeiotic treatment with indoleacetic acid there was some proliferation of gametophytic tissue.