LIFE HISTORIES OF ALGJE 239 



plant body of Ascophyllum becomes of very great interest. 

 Its cells possess the double or sporophytic number of 

 chromosomes, but it bears organs (spermagonia and 

 oogonia) that ultimately contain gametes. Is it, therefore, 

 a gametophyte or a sporophyte? For a long time it was 

 considered a gametophyte, but a clear understanding of 

 the divisions that take place in the gametangia, accom- 

 panied by reduction, and the fact that the body-cells are 

 all diploid, lead unmistakably to the conclusion that it is 

 a sporophyte. We have seen that the protoplasts of the 

 young spermagonium and the young oogonium are in 

 reality equivalent or analogous to spore-mother-cells, and 

 that, in each case, their four daughter-cells, with their 

 reduced number of chromosomes, are functionally equiva- 

 lent or analogous to spores. The spermagonia and 

 oogonia, therefore, which seem at first thought to be sexual 

 organs — simplified antheridia and archegonia — come to be, 

 finally, more truly comparable to sporangia, from which 

 the spores are not set free, as spores, but, while still in the 

 spore-case, develop into either a male or a female gameto- 

 phyte consisting of nothing but gametes. 



The real nature of Ascophyllum (and of the other 

 Fucaceae, for that matter) is just opposite from what a 

 superficial examination would lead us to infer, and we 

 have, in this low form, a condition just the reverse from 

 what is found in the liverworts, mosses, and ferns; in other 

 words, a prominent sporophyte, bearing a very simple 

 gametophyte, that lives upon it as a parasite deriving all 

 of its nourishment from the sporophyte. 



224. Alternation of Generations. — Although the game- 

 tophytic generation is reduced to its lowest terms, the 

 fundamental fact of alternation is not affected. As soon 



