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R. Ruggles Gates. 
CHAPTER IX. 
The Recapitulation Theory. 
The recapitulation theory has had many vicissitudes both in 
its application to plants and to animals. The conception has been 
stated and restated many times in varying terms, but that onto¬ 
genetic stages may have a phylogenetic significance has rarely been 
denied and has more often been implicitly assumed. The principle 
was tacitly recognized even before Darwin, and he accepted it 
practically without reserve. Indeed it was one of the foundation 
stones in his argument for evolution. 
It is desirable also to point out that any theory of recapitulation 
which is to have any significance in the interpretation of life 
histories must recognize that in the last analysis recapitulation 
implies that at some stage in the evolution of any group an increase 
in the life-cycle took place, by the addition of certain stages. This 
is in sharp contrast with a germinal change, which necessarily 
modifies every stage, at least internally as regards nuclear structure, 
but can hardly be held to add anything to the adult stage of 
development, or in other words to increase the number of stages 
in the life-cycle. 
Recapitulation and the alternation of generations in plants. 
As regards plants, it may first be pointed out that the theory 
of the antithetic alternation of generations, which has been widely 
adhered to by botanists and has been given its most notable 
expression in the classic volume of Bower (1908) on The Origin of 
a Land Flora , implies from the evolutionary point of view a 
continued lengthening and increase in complexity on the part of 
the sporophyte, and in seed plants a contemporaneous shortening 
and simplification of the gametophyte. This theory runs like a 
golden thread through all the speculations concerning the origin 
and larger relationships of the main groups of vascular plants, and 
there is nothing quite corresponding to it among animals. In the 
able hands of Bower, it implies that the sporophyte generation 
resulting from the fertilized egg is intercalated between two 
gametophyte generations and has gradually increased in complexity 
or length through the Bryophytes, Pteridophytes, Gymnosperms 
and Angiosperms in connection with their gradual transition and 
adaptation from aquatic or moist to typically terrestrial conditions* 
True, the theory of homologous alternation in plants has also 
been held, though not so widely. It was for a time based chiefly 
