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SCIENCE 



[N. S. Vol. XXXIX. No. 1000 



only, but also that the nuclei of the former 

 have twice as many chromosomes as those 

 of the sexual plants. He found also that 

 the number of chromosomes is reduced at 

 tetraspore formation and held that all this 

 cytological evidence indicated the alterna- 

 tion of the sexual and the tetrasporie 

 plants. The doubts of conservative botan- 

 ists regarding the regular and necessary 

 sequence of these haploid and diploid 

 plants were dissipated when Hoyt (1910) 

 raised fruiting tetrasporie plants from eggs 

 and mature sexual plants from tetraspores. 

 Hoyt thus demonstrated, for the first time 

 by cultures in any alga, the identity of this 

 alternation with that of the cormophytes. 

 Yamanouchi (1911 and 1913) has demon- 

 strated, cytologically and in part by cul- 

 tures, the occurrence of an exactly similar 

 type of alternation in the brown algoe 

 Cutleria and Zanardinia, the life cycle of 

 Cutleria seeming peculiarly like that of the 

 cormophytes because the two generations 

 dzf^^v not only in chromatin content, but 

 also in structure. 



In the red seaweeds also the use of cyto- 

 logical methods and the determination of 

 chromosome numbers has given a series of 

 very suggestive, though not as yet easily 

 interpreted, results. Oltmanns (1898) 

 showed that the nucleus of the carpospore 

 is a direct descendant of the diploid oospore 

 nucleus. Wolfe (1904) decided that in 

 Nemalimi, 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 fer- 

 tilized egg. He therefore follows Oltmanns 

 in regarding the diploid cell mass men- 

 tioned as the sporophyte of this species. 

 In a series of red algaj, which have a tetra- 

 sporie phase in the life cycle, Yamanouchi 

 (1906), Lewis (1909) and Svedelius (1911) 

 have demonstrated, cytologieaUy, an alter- 

 nation of two generations very similar in 



character to that first found 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 tetra- 

 sporie plants only. 



In the interpretation of the phenomena 

 seen in these red algae Yamanouchi regards 

 the tetrasporie plant as the more primitive 

 phase of the 2X generation, and carpospore- 

 formation as a sort of secondarily devel- 

 oped polyembryony for multiplying the 

 progeny from each fertilization. Lewis's 

 view, on the contrary, holds that the tetra- 

 sporie plant is, in origin, an early, self- 

 propagative phase of the primitive, hap- 

 loid, sexual generation. Further he sug- 

 gests that, in accordance with a general 

 tendency evident in many sexual plants, 

 the process of reduction has here been post- 

 poned, and pushed forward from the time 

 of carpospore-formation, where it still oc- 

 curs in the primitive form Nemalion, into 

 this originally haploid tetrasporie plant. 



Though no generally accepted interpre- 

 tation has yet appeared of the somewhat 

 varying chromosome cycles that have now 

 been elucidated in green, brown and red 

 algae, yet the mass of facts thus far obtained 

 presents an impressive picture of the essen- 

 tial identity of reproductive processes in 

 these plants with those found in the cormo- 

 phytes. Perhaps the most interesting point 

 noted in making such a comparison is the 

 fact that the type of life cycle among algae 

 that corresponds most closely with that of 

 an archegoniate, e. g., is the type found in 

 several genera of the brown algaj. The 

 fact may be recalled here also that it was to 

 the gametangia of this group that Davis 

 (1903) finally turned in his search for a 

 prototype of sexual reproductive organs of 

 the bryophytes. 



