ALTERNATION OF GENERATIONS. 4! 



plant generations is repeated an indefinite number 

 of times (repetitional generation), while the other 

 unlike plant generation appears only once and then 

 at the beginning of the resting stage and remains 

 latent in the form of a resting spore till the begin- 

 ning of the next period of generation. With this 

 peculiar transition generation, which has arisen in 

 the lower stages asexually, and in the following 

 higher stages by the union of a male and a female 

 cell, and which hence is hermaphrodite, there are 

 generally associated later two other single genera- 

 tions vis. , a generation preceding and one following 

 the hermaphrodite, the former as a sex-producing 

 generation, the other as a sex-produced generation. 

 The phylogenetic significance of the alternation 

 of generations consists in its representing a transi- 

 tion stage from the unicellular to the simpler multi- 

 cellular and from the latter to the more complex 

 multicellular plants. The plant generations of any 

 phylogenetic stage increase by ampliation, become 

 unlike by differentiation in time (alternation of 

 generations), and unite in a plant individual, whose 

 unlike ontogenetic stages correspond to the unlike 

 plant generations of the earlier ancestral series. 



22. MORPHOLOGY AS THE SCIENCE OF PHYLOGENY. 



All organic phenomena belong, according to 

 their causes, to two different classes: (i) Those 

 belonging to one group are the results of external 



