SEXUALITY IN PLANTS—JOHNSON. 399 
the number of chromosomes is reduced at tetraspore formation and 
held that all this cytological evidence indicated the alternation of the 
sexual and the tetrasporic plants. The doubts of conservative 
botanists regarding the regular and necessary sequence of these 
haploid and diploid plants were dissipated when Hoyt (1910) raised 
fruiting tetrasporic plants from eggs, and mature sexual plants from 
tetraspores. Hoyt thus demonstrated by cultures, for the first time 
in any alga, the identity of this alternation with that of the cormo- 
phytes. Yamanouchi (1911 and 1913) has demonstrated, cyto- 
logically and in part by cultures, the occurrence of an exactly similar 
type of alternation in the brown alge Cutleria and Zanardinia, the life 
cycle of Cutleria seeming peculiarly like that of the cormophytes 
because the two generations differ not only in chromatin content, but 
also in structure. 
In the red seaweeds also the use of cytological methods and the 
determination of chromosome numbers has given a series of very 
suggestive, though not as yet easily mterpreted, results. Oltmanns 
(1898) showed that the nucleus of the carpospore is a direct descend- 
ant of the diploid oéspore nucleus. Wolfe (1904) decided that in 
Nemalion, a species that does not form tetraspores, the reduction 
occurs at the budding out of the carpospores from the mass of cells 
arising by division of the fertilized egg. He therefore follows Olt- 
manns in regarding the diploid cell mass mentioned as the sporophyte 
of this species. In a series of red alge, which have a tetrasporic 
phase in the life cycle, Yamanouchi (1906), Lewis (1909), and Svede- 
lius (1911) have found cytological evidence of an alternation of two 
generations similar in character to that first seen in Dictyota. 
Lewis (1912) later proved conclusively by the use of cultures that the 
haploid sexual plants arise from tetraspores only, while the diploid 
fertilized egg gives rise, through the carpospores formed from it, to 
tetrasporic plants only. 
In the interpretation of the phenomena seen in these red alge 
Yamanouchi regards the tetrasporic plant as the more primitive 
phase of the 2X generation, and carpospore-formation as a sort of 
secondarily developed polyembryony for multiplying the progeny 
from each fertilization. Lewis, on the contrary, holds the view that 
the tetrasporic plant is, in origin, an early, self-propagative phase of 
the primitive, haploid, sexual generation. Further he suggests that, 
in accordance with a general tendency evident in many sexual plants, 
the process of reduction has here been postponed and pushed for- 
ward from the time of carpospore-formation, where it still occurs 
in the primitive form Nemalion, into this originally haploid tetra- 
sporic plant. 
Though no generally accepted interpretation has yet appeared 
of the somewhat varying chromosome cycles that have now been 
