Phylum Phaeophyta [ 93 



ducing eight. In Fucus, these become the nuclei of as many eggs. In other genera, 

 the number of functional eggs is reduced by degeneration of some of them, or of some 

 of the nuclei before cell division. In Sargassum, Kunieda (1928) found each oogon- 

 ium to produce a single egg in which seven nuclei undergo dissolution while one re- 

 mains to function. 



The first two nuclear divisions in each gametangium are meiotic. Farmer and 

 Williams (1896) and Strasburger (1897) showed that the bodies are diploid; Yama- 

 nouchi (1909) first gave a full account of the meiotic process. The haploid chromo- 

 some number of Fucus vesiculosus is 32. In Sargassum Horneri Kunieda found it to 

 be 16. 



By a swelling of colloidal material in the conceptacles, the gametangia are forced 

 out into the water, where they burst and release the gametes. Fucus was one of the 

 first organisms in which syngamy was observed. Thuret (1855) saw multitudes of 

 sperms swarm about the eggs, and showed that without sperms the eggs would not 

 develop. This much had already been observed in frogs and certain fishes; the dis- 

 covery that the essential process is the union of just one sperm with the egg was not 

 made until later. The growing zygotes give rise directly to diploid thalli. 

 ■ The gametangia of the Fucoidea appear to be homologous with the unilocular 

 sporangia of other brown algae. In the gametangia, as in unilocular sporangia, the 

 meiotic divisions are followed by a few divisions of the haploid nuclei: the Fucoidea 

 are not quite perfect examples of the reduction of the haplod stage to the gametes 

 only. As to which other brown algae may have provided their evolutionary origin, 

 there is no very satisfactory hypothesis; Sporochnus shows certain resemblances. 



