678 Lewis . — The Life History of Grijfthsia Bornetiana. 
the nucleus of each of these contains fourteen chromosomes. The nuclei 
of the tetrasporic plant contain each fourteen chromosomes ; and it there- 
fore seems reasonable to assume that the tetrasporic plants arise from 
carpospores. In the first division of the nucleus of the tetraspore- mother- 
cell the number of chromosomes is reduced one-half, so that seven chromo- 
somes enter the nucleus of each tetraspore. It seems probable that on 
germinating the tetraspore gives rise to an individual whose general 
morphological relations and vegetative structure are similar to those of the 
plant producing tetraspores, with two significant exceptions, ( 1 ) the nuclei 
show at mitosis seven chromosomes instead of fourteen, and ( 2 ) the indi- 
vidual bears sexual organs instead of asexual spores. In other words, in 
Griffithsia a sexual plant is probably succeeded by an asexual plant of 
similar morphological relations. 
The proof of this hypothesis must rest on actual cultural experiments, 
and it is much to be desired that such experiments be carried out 
Since Strasburger (78) showed that in the Archegoniates the double 
number of chromosomes is characteristic of the sporophyte and the single 
number of the gametophyte, the main facts have been confirmed in so 
many forms that many botanists have come to consider that the chromo- 
some number alone is a trustworthy guide for the identification of the two 
generations: that plants showing the diploid condition of the nucleus 
necessarily belong to the sporophyte, and that where the haploid condition 
of the nucleus obtains, the gametophyte is necessarily involved. Botanists 
have come to speak of the sporophyte as the ‘ 2 ^-generation ’ (Lotsy, 51), 
and of the gametophyte as the ‘ ^-generation ’ ; and undoubtedly within the 
Archegoniate series such a conception is very useful. However, even in 
Archegoniates, where the rule is so generally applicable, recent work tends 
to show that the diploid condition of the nucleus is not necessary for the 
differentiation of the sporophyte (Yamanouchi, 94), nor is the haploid con- 
dition necessary for the differentiation of the gametophyte (Farmer and 
Digby, 30). 
In thallophytes, the evidence at hand indicates great diversity in the 
point at which the numerical reduction of chromosomes takes place. Even 
in the single group of Rhodophyceae the point of reduction occurs at 
different places in the life-history of different species. When one comes, 
therefore, to regard the chromosome number as the sole test for the delimi- 
tation of sporophyte and gametophyte, it seems probable that confusion will 
result. With this in mind I shall now review briefly the opinions 
expressed by workers in this field as to the alternation of generations in the 
red algae, and shall venture to offer some suggestions as to the meaning 
of the rather complicated nuclear life-histories of members of this group. 
Oltmanns (58), after a careful study of the development of the cysto- 
carp in four genera, came to the conclusion that the sporogenous cells 
