CHAPTER FOURTEEN. 

 ALTERNATION OF GENERATIONS. 



1. Summary of Reproductive Methods. We may class 

 the methods of reproduction that have been studied as 

 follows: 



1. Those that occur without union of gametes, as in 

 fission, budding, spore formation, etc. (non-sexual). 



2. Those that involve union of gametes, whether 

 similar or unlike (sexual). 



We have studied many forms of plants and animals in 

 which both non-sexual and sexual reproduction are found. 

 For example, hydra buds and also produces eggs and 

 sperms; many of the algae reproduce both by swimming 

 spores and by gametes. In the forms referred to, however, 

 we must note one important fact: the final organisms 

 produced by the tv/o methods were alike. We could not 

 tell by looking at an individual hydra whether it had been 

 formed as a bud or had come from a fertilized egg. 



2. Alternation of Generations. There is another step in 

 the story which we must now master. It often happens 

 that this reproduction by union (sexual) and reproduction 

 without union (non-sexual) occur in the same species, in 

 regular alternation, as we have seen in mosses and ferns. 

 Furthermore, the individual that results from non-sexual 

 reproduction is different from the individual formed by 

 the union of gametes, usually so different that no one 

 would take them as belonging to the same species. This 

 is called alternation of generations. If we illustrate by 



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