74 HOLISM AND EVOLUTION chap. 



this phase of reproduction must have developed before the 

 separation of plant and animal forms took place. It forms 

 also the basis for that alternation of generations which is 

 one of the most remarkable of all the phenomena of life. 

 Thus all organisms which are reproduced through cell-fusion 

 have a generation in which the cells have the single contents 

 (after the reduction division) and another in which the cells 

 have the double contents (before the reduction division). In 

 the higher forms of plants and animals the generation of the 

 single-content cell, or the gametophyte generation as it is 

 called, is reduced to a very subordinate role and a short 

 life, as it covers the short period of the gametes or conjugat- 

 ing cells (the ripe sperm-cells and ova) in flowering plants 

 and in the more developed animals. The generation of the 

 double-contents cell, or the sporophyte generation as it is 

 called, has become dominant and appears as the developed 

 plant or animal which we see in nature to-day. But in some 

 divisions of plants the gametophyte generation is still of 

 some prominence. Thus the moss plant is the gametophyte 

 generation, the sporophyte generation appearing as a sub- 

 ordinate parasitic form. And in the ferns, where the sporo- 

 phyte is the dominant form, the gametophyte appears as a 

 distinct plant which is in some cases a perennial. And its 

 relation to the fern was quite unknown until about the 

 middle of the nineteenth century. 



This generation of the single-content cell, or the gameto- 

 phyte in the developed plants and animals of to-day, is 

 interesting because it probably illustrates the well-known 

 principle that ontogeny repeats phylogeny, that is to say, 

 that the history of the individual organism recapitulates in 

 its earlier or embryonic stages of development the various 

 phases of development through which its types of ancestors 

 have evolved in the past. Thus the gametophyte generation 

 is a reminder of that earlier, simpler, more primitive phase in 

 plant evolution when the more complex sporophyte genera- 

 tion, which is dominant to-day, had not yet been evolved 

 through cell-fusion in reproduction. And it is even possible 

 that the form of the present gametophyte may throw light 



