The Life-history of Colpomenia sinuosa (Scytosiphonaceae), with Special Reference to the Conjugation of Anisogametes.

Abstract

1. Colpomenia sinuosa (ROTH) DERB, et SOL., (Scytosiphonaceae) which is found on branches of Sargassum in the sea around Misaki was used for our observations. It grows abundantly in spring and in autumn.
2. The pleurilocular sporangia are formed on the plant of Colpomenia which grows in autumn. The zoospores liberated from them are fusiform, measuring about 5-6μ×3μ.
They germinate without conjugation and give rise to the protonemas on which many young plants of Colpomenia were observed after about five months (in January or February of the next yeas).
3. The plants of Colpomenia collected in spring are dioecious, having a more remarkably differentiated sexuality than those observed in other plants of Scytosiphonaceae.
Two kinds of the pleurilocular sporangia are also formed on the male and female plants, showing a difference in structure.
4. There is considerable difference in size and form of two gametes of different sexes. The female gamete is about 9-10μ×4-5μ and has a yellowish green chromatophore with reddish eye-spot.
The male gamete which has a reddish eye-spot is much smaller than the female one, measuring about 5μ×2μ. No chromatophore is observed in the male gametes while some of them have green granules.
5. When the gametes of different sexes meet, some male gametes are attached to a single female gamete, forming a conjugating group which somewhat resembled a so-called“Kranzenbildung”observed by BERTHOLD in Ectocarpus.
A zygote germinates, giving rise to a protonema. After that no further changes were observed. The female gamete also germinates without conjugation, giving rise to a protonema but no change is observed in the male gamete.
6. From the present investigation it is possible to suppose that in Colpomenia sinuosa the plant collected in autumn is the sporophyte while the plant collected in spring is the gametophyte.