LIFE HISTORIES OF ALG^E 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 reduced to 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 greatly simpli- 
fied 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 
