682 Lewis . — The Life History of Grijfthsia Bornetiana . 
gametophyte (the sexual plant) with the antithetic sporophyte (the sporo- 
genous cells of the cystocarp), there is a succession of homologous phases, 
inasmuch as a tetrasporic individual regularly succeeds a sexual individual 
of identical morphology. This latter condition is not paralleled in the 
Archegoniate series ; and since the terms gametophyte and sporophyte 
have come to have a special significance in connexion with such conditions 
as are found in the Archegoniates, neither of these terms should be applied 
to the tetrasporic plants of Griffithsia and Polysiphonia . The tetrasporic 
plant has probably been intercalated in the life-history of the red algae, but 
there is no evidence for the belief that it has been intercalated by gradual 
integration and differentiation of a simple product of the germination of the 
zygote, which product was at first unlike the sexual plant and which 
represents a new departure in the life-history ; and the intercalation, 
by amplification, of an unlike phase seems to be the very pith of the 
theory of antithetic alternation (see Bower, 11 ; and 12, p. 47 ; Yamanouchi, 
94, p. 310). 
According to this view, the tetrasporic plant probably arose, when first 
produced, with the complete differentiation characteristic of this species. 
The best evidence for this conclusion is based on the morphological identity 
of the tetrasporic with the sexual plant. Similar environmental conditions 
would hardly suffice to produce identity of form in two individuals unless 
the individuals were from the beginning identical. The tetrasporic plant 
of a red alga may be said, then, to be homologous with the sexual plant. 
That the two phases are homologous is evidenced, not only by their 
similarity of structure, but by the fact that either seems capable of pro- 
ducing the morphological equivalent of the reproductive structures of the 
other. It has been known since Bornet first called attention to the fact (10) 
that in many species of red algae structures resembling tetraspores are occa- 
sionally found on the sexual individuals. This phenomenon has been 
carefully investigated in Polysiphonia violacea and Griffithsia Bornetiana . 
In Polysiphonia , Yamanouchi (93) found that the development of these 
tetraspore-like structures ceases at the mother-cell stage ; cleavage of the 
cytoplasm may begin, but normal nuclear division is absent In Griffithsia , 
the phenomena observed are similar to those noted in Polysiphonia , except 
that by the time the abortive cleavage begins, the nucleus has divided to 
form several. The cleavage planes have never been observed to reach the 
centre of the cell, and it is quite evident that tetraspores are not formed, 
since the whole cell becomes withered and wrinkled, resembling the 
degenerated tetrasporangia described on p. 668. In one instance, however, 
a mother-cell was observed in which no trace of cleavage of the cytoplasm 
was apparent, and in which the number of nuclei had increased to sixteen, 
the whole structure resembling very much the early stages of germination 
of a normal spore. It seems quite possible that the tetraspore-mother-cells 
