8 M. Tahara. • 



in Fucaceae^^ in Sargassum and CystophyUwn one can not observe 

 several developmental stages of the oogonium in the same con- 

 ceptacle. Not only the same conceptacle, but also all the materials 

 collected on the same place, on the same day, do not show in 

 general the several developmental stages of the oogonium. 



After the occurrence of an oogonium liberation, the single 

 nucleus of the oogonium, which is to be liberated for the next 

 period, remains in a resting condition for a time and for the first 

 time on the day before the day of the next oogonium liberation, 

 the nucleus begins to divide to form the nuclei of oosphères, and 

 the oogonium attains the di- or tetra-uucleate condition. On the 

 day of the liberation, the oogonium contains eight nuclei evenly 

 distributed in its substance; the dense mass of chromatophores 

 assembled around each nucleus facilitates the counting of the 

 number of the nuclei. Fig. 1, PL. II, Fig. 3, PL. Ill show this 

 condition of the oogonium in S. Horncri and Cyst, sisymhrioidcs re- 

 spectively. Nienburg' s recently published paper on C y stoseira and 

 Sargasswir^ states also that three successive nuclear divisions take 

 place in the oogonium before the formation of oosphères. While 

 the result of my observations is based on living materials, 

 Nienburg made his study on the microtome-sections of fixed 

 materials. At aii}^ rate the occurrence of the three successive 

 nuclear divisions in the oogonium development seems to be general 

 in Fucaceae. The eight nuclei formed in one oogonium have at 

 first the same appearance. But Sargassum and CystophyUwn develop 

 only one egg in one oogonium, so ouly one of the eight nuclei 

 becomes the functional nucleus of the oosphères and the others are 

 destined to degenerate in the course of future development. Fig. 

 4, PL III shows a stage in which some of the eight nuclei are 

 about to degenerate. The degeneration of the seven nuclei does 

 not proceed simultaneouly. 



In other Fucaceae the superfluous nuclei are regularl}^ thrown 

 out into the space between the oogonium wall and the oosphère. 

 But it seems to me that this is not the case in Sargassum and 



1) Oltmanns, Beiträge zur Kenntnis der Fucaceae, Bibl, Bot. 1889. p. 84. 



2) Nienburg, Die Oogonentwicklung bei Cystoseira und Sargassum. Flora Bd. I. 1910. 



