Der Lebenszyklus vonAcrosiphonia grandis (Acrosiphoniales, Chlorophyta)

Abstract

Acrosiphonia granlis Kjellm, is well characterized by its long rows of intercalary fertile cells. Material obtained from Iceland proved to be very interesting by reason of its peculiar life history. The zygote develops into a codiolum-like stage, which grows directly into anAcrosiphonia thallus at an age of some 20 days without formation of swarmers. The same features have recently been demonstrated byJónsson (1967) in an Icelandic species, identified by him asAcrosiphonia sonderi. From his specimensJónsson described facultative caryogamy, ascertained by him formerly in otherAcrosiphonia species: its absence induces the above-mentioned development, giving rise to a generation of mictohaplonticAcrosiphonia. In contrast, true zygotes of “Acrosiphonia sonderi” develop into fertile codiolum cells, reproducing themselves by biflagellate swarmers. InA. grandis, facultative caryogamy has not been observed and nuclear fusion occurs in all zygotes. Codiolum stages never produced swarmers. The life history ofA. grandis represents an intermediate type between the heteromorphic cycle of species such asA. spinescens (including a true codiolumsporophyte), and the isomorphic life history ofA. arcta, where the zygote develops directly into the filamentous plant.

Zusammenfassung

• 1. Acrosiphonia grandis Kjellm. ist morphologisch durch die gereihte Anordnung ihrer fertilen Zellen gut gekennzeichnet.

• 2. Aus den Zygoten entsteht ein Codiolum-artiges Stadium, das sich ohne fertil zu werden im Alter von etwa 24 Tagen unmittelbar zu einer neuenAcrosiphonia-Pflanze entwickelt.

• 3. Zweigeißelige positiv phototaktische Schwärmer entwickeln sich in gleicher Weise, jedoch stark verzögert.

• 4. Fakultative Karyogamie konnte beiAcrosiphonia grandis nicht beobachtet werden.