*9° BOTANICAL GAZETTE [ MARCH 



antheridium 



com 



in the higher plants, and that the four nuclei in these structures thus 

 produced may be compared with microspores and megaspores, which 

 in Fucus germinate at once within the oogonia and antheridia, 

 and the gametophyte generations, thus initiated, undergo only one 

 mitosis in the oogonium and four mitoses in the antheridium. Thus 

 in Fucus the gametophyte generation with the haploid number 

 extends from the tetranucleate stage both in antheridium and oogo- 

 nium initials, up to the formation of the sperm and egg. With the 

 union of the gametes, the sporophyte generation with the diploid 

 number of chromosomes begins, and it terminates with the develop- 

 ment of the four nuclei in the antheridium and oogonium initials. 



SUMMARY 



The nuclear conditions during the life-history of Fucus vesiculosa 

 may be summarized as follows: 



i. The Fucus plant contains 64 chromosomes and the number i 

 reduced at the end of the first two nuclear divisions in the oogonium 

 and antheridium initials. 



2. Each of the four nuclei produced at the end of the first two 

 divisions contains 32 univalent chromosomes, and this number 



formation 



1 7™ "F w L "e iormation ot the sperm and egg; trie pnase w» 



taming 32 chromosomes may be regarded as the gametophyte gen- 

 eration. 



3- The union of the gametes doubles the number, and 64 chromo- 

 somes are present in every mitosis through the development of the 

 Fucus plant up to the formation of the first four nuclei in the oogonium 

 and antheridium initials. The phase containing 64 chromosomes 

 may be regarded as the sporophyte generation. 



4- There is thus present in Fucus an alternation of the gameto- 

 phyte generation containing 32 chromosomes, with the sporophyte 



The University of Chicago 



»mes 







