Notes on Recent Literature. 
2 14 
of generations. Previously to these discoveries there had been a 
tendency to regard the carpospore-bearing (i.e., the immediately 
post-zygotal) phase of the life-history of Floridese as the equivalent 
of the “ sporophyte” of archegoniates and more particularly as the 
equivalent of the sporogonium or fruit-body of the Bryophytes. By 
the upset of that comparison, so far as the cytological correspondence 
of carpospores and archegoniate spores was concerned, the value of 
certain evidence for the theory of the antithetic origin of alternation 
of generations in the Pteridophyta was pro tanto weakened, though, 
as has often been pointed out, that theory cannot be disproved by 
any evidence ot this class. 
The recently published results of Svedelius on Delesseria and 
of Lewis on Griffithsia , Polysiphonia and Dasya, entirely confirm 
those of the previous workers and suggest that the diploid character 
of the tetrasporic individuals of Florideae, correlated with meiosis 
at formation of the tetraspores, is quite general. 
Svedelius (1911) shows that the nuclei of the tetrasporic plants 
of Delesseria sanguined have the diploid number of chromosomes (40), 
while the sexual (demonstrated only in the female) plants have the 
haploid number (20), as have the tetraspores themselves, the 
formation of tetraspores showing the typical phenomena of tetrad 
or reduction-division, with synapsis, and a heterotypic followed by 
a homotypic division. 
Lewis (1909) showed in Griffithsia that the zygote nucleus, the 
carpospore nuclei and the nuclei of tetrasporic plants all contain 
14 chromosomes, while at the first division of the nucleus of the 
tetraspore mother-cells the number of chromosomes is reduced to 
one-half, each tetraspore nucleus containing 7 chromosomes. 
In a later paper the same author (1912) shows by means of 
cultural experiments in which the plants were allowed to develop 
in the open sea that the carpospores of Polysiphonia violacea produce 
tetrasporic plants only, while the tetraspores of Griffithsia Bornetiana 
and Dasya elegans produce sexual plants only. 
Thus the occurrence of a regular alternation of tetrasporic 
with sexual plants, the diploid nature of the nuclei of the former, 
and the occurrence of meiosis at the production of tetraspores is 
now established on a much broader basis. 
Now since, as Lewis remarks (1909, p. 682), “the intercalation 
by amplification of an unlike phase seems to be the very pith of the 
theory of antithetic alternation,” the establishment of this fact, that 
the cytological alternation takes place not between the independent 
vegetative plant and the carpospore-bearing fruit-body, but between 
the sexual plant and the tetrasporic plant phis the immediately 
preceding carposporic phase, introduces a new complexity into the 
attempted comparison with the Archegoniates. In the case of 
Dictyota, where there is no carposporic phase in the life-history, a 
direct comparison obviously suggests a homologous origin of the 
phenomenon of alternation, since the two cytologically differing 
generations are vegetatively alike and it is gratuitous to suppose 
that one of the two has been “intercalated” in the life-history. 
It is much simpler to regard the two generations as homologous by 
descent, the production of the two kinds of reproductive cells having 
been originally, as in the lower Algae, entirely under the control of 
external conditions, and having now become localised in the two 
