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A study of Codium fragile Borden, Carol Ann


Codium fragile (Suringar) Harlot (Chlorophyta, Codiales) is a siphonous marine alga of extensive distribution and varied habitat. Ordinarily It is described as reproducing sexually, by fusion of anisogamous gametes produced on separate individuals. However, there are populations reported which consist exclusively of female plants reproducing by parthenogenetic germination of female gametes. Three aspects of the biology of a population of Codium fragile from Vancouver Island, British Columbia, were studied. (1) Zygotes and germlings were obtained in cultures in the laboratory and their growth and early development were observed. No utricles were produced by young germlings, even after three to four months in culture; the existence of a "juvenile filamentous stage" without utricles is suggested. The possibility of parthenogenetic development of female gametes was investigated and it was found that, in the material studied, zygotes and germlings are produced only in the presence of both male and female plants. (2) Apical segments of C. fragile 2.5, 3.5 and 4.5 cm in length were treated with 5 mg/l IAA. IAA-treated 4.5 cm segments showed a slight but significant increase in growth over controls. No such increase was found in IAA-treated 2.5 and 3.5 cm segments. (3) The mitotic cycle and the periodicity of mitosis in germlings in culture were investigated. In most respects mitosis in C. fragile resembles "normal" mitosis. However, a persistent nucleolus-like body was observed during all stages of division. Attempts to ascertain the chemical nature of this body were unsuccessful. Experiments on the periodicity of mitosis disclosed a series of peaks of mitotic activity which appear to be unrelated to the time of onset of light or darkness. Mitosis within any one germling is asynchronous.

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