Alternation of Generations in Relation to Reduction Division

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Abstract
The paper contains a discussion of the problem of the alternation of generations in plants and its relation to the reduction division. The author claims that the alternation of generations can not be regarded as an exclusively morphological problem but must be regarded in combination with the fertilization as well, with its complement the reduction division. Primitive types of alternation of generations are those with 1 reduction division immediately after the fertilization, thus 1 fertilization[long dash]1 reduction division, whereby never more than 2 chromosome combination possibilities can be realized; but when a more or less highly developed diploid sporophyte is formed, which produces numerous spore mother cells, each of which undergoes reduction division[long dash]that is, when 1 fertilization is compensated by many reduction divisions[long dash]then numerous combination possibilities are sure to be realized. The development of a diploid sporophyte, due to the delay of the reduction division, then secures to the plant the possibility of bringing about numerous reduction divisions and thereby numerous character combinations. Thus it is more advantageous to the plant to become diploid than to remain haploid, and in fact the systematically highest types are all diploid. This hypothesis has the advantage of being a general explanation of the rise of the alternation of generation in all groups independently of their external conditions of life. The migration theory of Bower and Wettstein, that looks upon the antithetic alternation of generations as evolved only in connection with the migration of plants to land, is rejected, as we have now discovered precisely the same development in the direction of the predominance of the sporophyte in marine algae which never have migrated onto land, viz., the Phaeophyceae (Ectocar-pales, Laminariales, Fucales).

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