224 
R. Ruggles Gates. 
which appears to be well justified by the facts. The life history of 
Griffithsia is in general parallel to that of Polysiphonia, the tetra- 
sporic plants apparently having 14 chromosomes and sexual plants 
7, though there is some doubt about the accuracy of these counts. 
According to the views of Lewis, there is (1) an antithetic 
alternation between sexual plants, representing the gametophytes, 
and the sporogenous cells of the cystocarp, representing the sporo- 
phyte, (2) a regular succession of tetrasporic and sexual individuals 
representing an homologous alternation of generations but not 
equivalent to the alternation in Archegoniates. He believes that 
the tetrasporic plant has been intercalated in the life history, not 
through the “gradual differentiation of a simple product of the 
germination of the zygote,” which is the pith of the antithetic 
theory; but, as Yamanouchi suggested, through the suppression of 
chromosome reduction in the formation of a carpospore which then 
at once grew into a tetrasporic plant. 
In concluding a brief survey of this very large subject of alter¬ 
nation, we may remark that the antithetic theory, which continues 
to receive the larger number of adherents, implies just such a 
lengthening of the life-cycle as is indicated by recapitulatory 
phenomena. The homologous theory, on the other hand, would 
account for the alternation through the sudden intercalation of a 
generation in Algae as the result of a change in spore development 
which is essentially mutational. In Archegoniates, the homologous 
view would apparently imply the gradual simultaneous progressive 
differentiation of gametophyte and sporophyte through differences 
in the environment in which the asexual spore and the fertilized 
egg develop. But as Farmer 1 has pointed out, it is impossible to 
imagine how the Bryophyte sporogonium at any rate could have 
arisen through modification of the gametophyte. It seems clear 
that this structure at least must represent an intercalated phase 
progressively developed. Each group of plants must then, as 
Farmer has emphasized, be separately considered on its own merits, 
on the basis of the historical probabilities as determined by 
comparative morphology. 
Recapitulation phenomena in Gametophytes. 
It may be noted in passing that although plants “ climbed out of 
the water ” at a remote period, yet large groups of Bryophytes and 
Pteridophytes still survive although imperfectly adapted to life on 
dry land. This, as Bower points out, is probably because the 
1 New Phytol. 8: 113, 1909. 
