Phänoembryoiogie der Hochgebirgspflanzen Saxifraga oppositifolia und Cerastium uniflorum

Abstract

Summary The morphological and temporal course of embryogenesis and seed development of Saxifraga oppositifolia and Cerastium uniflorum during the entire growing season were studied in their natural high-mountain habitat and were related to the sequence of rcproductive phenology. At short intervals, buds, flowers and fruits were collected from the same individual. Thc cleared ovules and immature seeds were examined and measured microscopically using the interference contrast technique. S. oppositifolia blooms as soon as the snow has melted. Immediately before the flowers open, the ovules are in the post-meiotic state and are not ready for fertilization, until the flowcrs are fully open. After fertilization there is a delay of 2 — 3 weeks before development of the helobial endosperm begins. The embryogeny is of the Caryophyllad type. In all, the differentiation and ripening of the seeds take a total of 11 weeks. C. uniflorum flowers in summer on the new shoots approximately a month after the snow has melted. The campylotropic ovules are already prepared for fertilization when the flowers open, and continue their development without delay after fertilization. Embryogenesis proceeds according to the Caryophyllad pattern. The storage tissue is a perisperm, the endosperm being restricted to a single layer surrounding the embryo. After 5-6 weeks the embryonic organs are developed; growth of the embryo continues for a further 2 wecks. The specific reproduction period, i.e. the time elapsing between fertilization and [mal differentiation of the seeds, amounts to 70-80 days in S. oppositifolia and about 40 days in C. uniflorum. S. oppositifolia can come into flower very early because the flower buds are almost completely differentiated in the previous year; in the spring, the plant's rich stores oflipids are available for flowering and formation of new shoots. Fruit sct coincides with expansion of the shoots and roots. In C. uniflorum , however, the assimilatory organs have first to develop before they can deliver the energy needed for flowering and the rapid development of seeds. If in C. uniflorum the vegetative phase before onset of the reproductive period is included, both species require 10-11 weeks of favourable weather for their annual seed production.