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THE AMERICAN NATURALIST [Vol. LII 



the groups considered as units are fundamentally distinct, 

 but it is doubtful whether any such implication would be 

 admitted by the majority of its users. In fact one could 

 hardly maintain that simple division, sporification, the 

 production of gemmules, true budding, fragmentation 

 with regeneration of parts, and the various kinds of 

 apogamy and parthenogenesis on the one hand, and all 

 nuclear fusions on the other, can be grouped together as 

 if they are of the same evolutionary value, if this term be 

 used in any narrow or special sense ; but from a broader 

 viewpoint, the conventional classification has a real and 

 deep meaning' which perhaps the biologist has grasped 

 instinctively. 



There are both asexual and sexual methods of repro- 

 duction in nearly all groups of animals and plants ; among 

 animals the second has almost supplanted the first, among 

 plants the two have continued side by side. In neither 

 kingdom was sex developed as a more rapid means of 

 multiplication, since, as Maupas showed, a single infuso- 

 rial! may become the progenitor of some 50,000 individuals 

 during the time necessary for one pair to conjugate. 

 Some other requirement was fulfilled; and fulfilled ade- 

 quately if we may judge by the number of times sexual 

 differentiation arose and the tenacity with which it was 

 retained. 



Just when sexual reproduction first originated in the 

 vegetable kingdom is still a question. Among the lower 

 forms only the schizophytes, flagellates and myxomycetes 

 have passed it by. Perhaps it is for this reason that 

 these forms have remained the submerged tenth of the 

 plant world. It is tempting, as Coulter (1914) says, to 

 see sex origin in the Green Alga-. There, in certain 

 species, of which Ulothrix is a good example, spores of 

 different sizes are produced. Those largest in size germi- 

 nate immediately under favorable conditions and produce 

 new individuals. Those smaller in size also germinate 

 and produce new individuals, but these are small and 

 their growth slow. Only the smallest are incapable of 



