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tion of two alternating generations, of which the one bears the 

 asexual organs on the upright system, and the other bears the 

 sexual organs on the creeping base. Disappearance of the base 

 in the former and of the upright system in the latter (both 

 phenomena which are known to occur among the Chaetophorales) 

 will give two different generations, resembling those of the 

 Archegoniatae in all essential respects." * * * "Such an origin, 

 of course, amounts to an homologous one, though presumably 

 of a somewhat different kind to that in the minds of the adherents 

 of the homologous theory." 



To Dr. Fritsch's theory as here formulated, two possible 

 criticisms suggest themselves. The first and probably less serious 

 of these criticisms is that thus far there seems to be no experi- 

 mental evidence of any tendency towards an alternation of 

 generations in Trentepohlia or in any other member of the order 

 Chaetophorales. If the divergence of the prostrate sexual part 

 and the erect asexual part was accompanied by each of these 

 parts reproducing itself and not the other, which seems equally 

 plausible, a priori, the final result would manifestly be what 

 systematists would call two independent species. But it is, of 

 course, conceivable that such a segregation and divergence as 

 this may have occurred more or less parallel with a movement 

 that resulted in an alternation of generations. 



The second and probably more serious criticism is that the 

 theory seems to give insufficient consideration to the fact that 

 the cell-nuclei of the so-called sporophyte in the Archegoniates 

 have twice as many chromosomes as do those of the gametophyte. 

 Now the diploid and haploid relation of the chromosomes in 

 sporophyte and gametophyte in the Archegoniates is so easily 

 and obviously associated with the fusion of two gametes and the 

 halving of the resulting chromosome number that it is almost 

 inconceivable that it should have come about in any other way. 

 Any supposition that the cell-nuclei of the hypothetical general- 

 ized ancestor may have had 28, 29, 30, or possibly a variable and 

 indefinite number of chromosomes and that in purely vegetative 

 ways the cells of one generation came to have always 20 chromo- 

 somes while those' of the other came always to have 40 chromo- 



