Febeuaey 27, 1914] 



SCIENCE 



311 



zygote in these forms, though chromosomes 

 could not be counted. Not till very re- 

 cently was it demonstrated for one of these, 

 Spirogyra, that the chromosome number is 

 actually reduced at this time. Trondle 

 (1911) has counted chromosomes of Spiro- 

 gyra and finds that there is a real reduc- 

 tion here, and that three of the first four 

 nuclei formed in the zygote degenerate, the 

 fourth remaining as the nucleus of the 

 single embryonic plant formed. 



In a study of the green alga, Coleochcete, 

 Allen (1905) showed that the chromosome 

 reduction occurs with the beginning of 

 germination of the zygote. Hence the 

 group of zoospore-producing cells, arising 

 from the latter, is not to be regarded as a 

 sporophyte, as had often been maintained. 

 Allen thus eliminated the only ancestral 

 prototype of the bryophyte sporogonium 

 that the antithetic alternationists had been 

 able to discover among the green algse. 



The search among the brown algiE for 

 parallels to the chromosome history of the 

 cormophytes has been much more success- 

 ful. The first case made out, that of Fucus, 

 by Farmer and Williams (1896) and by 

 Strasburger (1897) seemed, it is true, not 

 very illuminating. They found the reduc- 

 tion occurring in the first divisions of the 

 eggs and sperm-producing organs, a point 

 where it occurs in no other green plant. 

 This case of Fucus, you will remember, is 

 the one used by Scott (1896) to point a 

 moral, when voicing the generally felt crit- 

 icism of those botanists who proposed 

 "making the number of chromosomes the 

 criterion by which the two generations are 

 to be distinguished. ' ' He says : 



I venture to think it premature to rush into in- 

 ductive reasoning from imperfectly established 

 premises. The case of Fucus in which the Fucus 

 plant is shown to have the full number of chromo- 

 somes goes dead against the idea that the sexual 

 generation (and who could call a Fucus plant any- 

 thing but sexual) necessarily has the reduced 



number of chromosomes. This fact is indeed a 

 rebufE to deductive morphology. 



When, however, Strasburger (1906) and 

 Tamanouchi (1909) followed out the log- 

 ical trend of the chromosome evidence un- 

 reservedly, this life history of Fucus be- 

 came more readily comparable with that 

 of the cormophytes and with those of cer- 

 tain brown and red algae that had in the 

 meantime been elucidated by Williams and 

 Tamanouchi. From this point of view, 

 elaborated by Tamanouchi, the Fucus 

 plant with its 2X number of chromosomes 

 is a sporophyte and the reproductive 

 organs arising in its conceptacles are sjm)- 

 rangia comparable with those of a seed 

 plant. After the reduction, which occurs 

 at the normal point, at sporogenesis, each 

 of the four megaspores, without escaping, 

 gives rise to a gametophyte of two fertile 

 cells or eggs. Each of the four microspores 

 in turn forms a gametophyte, or X genera- 

 tion, of but sixteen cells, each of which ia 

 fertile and forms a spermatozoid. J* is 

 interesting to note here the similarity 

 which has been pointed out by Strashr.rgc :r 

 and by Chamberlain of the chromosome 

 cycle of Fucus to that of animals. In the 

 latter, from the plant cytologist's point of 

 view, the sexual generation has become re- 

 duced to the four haploid nuclei formed at 

 spermatogenesis and oogenesis ; and the so- 

 called ovary and spermary are really spore- 

 producing organs of the 2X or asexual 

 generation. 



In the brown seaweed Dictyota the dis- 

 covery of the chromosome cycle revealed, 

 for the first time in any thallophyte, an 

 alternation that seemed clearly comparable 

 with that of the cormophytes in this re- 

 spect. Williams (1904) was able to show 

 that the morphologically similar, mature 

 plants of Dictyota dichotoma differ not 

 only in that some produce spores only and 

 others male or female reproductive cells 



