The life cycle of Ralfsia clavata and R. borneti

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Abstract
The life cycle of Ralfsia clavata (Harvey) Crouan and R. borneti Kuckuck has been completed in culture. In both organisms the sequence and morphology of the various stages were similar, and these two species are considered as a single entity. Zoospores from unilocular sporangia of the crustose stage in nature gave rise to two morphological forms: (1) crustose thalli with erect filaments, paraphyses, and unilocular sporangia; (2) branched, uniseriate filaments with discontinuous parenchymatous areas and unilocular sporangia. Petalonia-like, thalli, which produced embedded plurilocular sporangia characteristic of the genus Petalonia, were initiated from both the crustose and filamentous forms. Fusion was not observed, and swarmers from both uni- and pluri-locular sporangia gave rise to the crustose and filamentous forms. On the basis of these results, and other culture studies, these two species of Ralfsia are merely stages in the life cycle of species of Petalonia.
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