1) The sexual reproduction by the biflagellate gametes of a
Prasiola species, which is probably
Prasiola japonica Yatabe, was discovered.
2) Formation of the round thick-walled gonidia and the microscopic crenated gemmae are discovered on the margin of the frond grown out of zygote.
3) By the experiment of germination of zygotes which are made to attach to a stone, remarkable increase by asexual reproduction is ascertained.
3) Enlarged round gonidia are extruded as the naked undivided aplanospores (av. 13μ in diameter). The mode of germination of aplanospores is the same as that of the full-grown zygotes. This feature is different from the “tetraspores” (6-8μ in diameter) reported by Lagerheim which have already undergone vertical and horizontal divisions. The fronds grown out of the cultured zygotes get perforated after losing the aplanospores and eventually disappear from September to October.
5) The fronds derived from the aplanospores form also the aplanospores on the margin, and this may be repeated. Finally the gametangia are formed. In late November they begin to liberate the gametes.
6) Young fronds and the microscopic sporelings are found chiefly from April to November. Even a young frond which measures about 1cm in length already has the aplanospores in the best condition.
7) Increase of
Prasiola is mainly due to asexual reproduction. From July to November they go on in quantity.
8) Although there are both sexual and asexual reproduction in
Prasiola, alternation of nuclear phase may not exist, since the gametes are liberated from the frond just forming aplanospores.
9) The life-history of
Prasiola in the Mitsusawa is considered as follows: ‘The zygotes begin to germinate after increasing in size. The growth of their sporelings continues, forming aplanospores on its marginal parts. After the asexual reproduction by aplanopores has been repeated, the gametangia are formed on these fronds. The liberation of the gametes extends from late October to late April next year, then they lost from sight. But by this time the fronds derived from the zygotes are already growing.’
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