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Bower (1890) viewed the alternation of generations of archegoniates as arising from the adaptation of an initially aquatic organism for the land.
(Overton believed that the reduction of chromosome number occurred at synapsis not, as we now know, in the subsequent nuclear division.) He wrote, "It will be a matter of great morphological as well as physiological interest, to establish beyond the possibility of a doubt that the alternation of generations, which is so remarkable a feature in the life-history of plants, is dependent on a change in the configuration of the idioplasm; a change, the outward and visible sign of which is the difference in the number of the nuclear chromosomes in the two generations."
Debates about alternation of generations in the early twentieth century can be confusing because three ways of classifying 'generations' co-exist (sexual vs.
An argument often put forward in favor of the homologous theory of alternation of generations (and sporophyte origin) is the alleged "evidence" of algae with isomorphic (morphologically identical or very similar) gametophytes and sporophytes, such as Ulva, Cladophora suhriana, Chaetomorpha (cf.
246) presented an easy-to-follow "flow diagram" of the evolution of meiosis, life cycles, alternation of generations, and so forth; their tracings led first to eukaryotes (after the development of mitosis and meiosis), and then to several major eukaryotic lineages and sublineages, including land plants based on the timing of meiosis in the life cycle and the supposed development of alternating generations.
South and Whittick (1987) rightly saw land plants as possessing sporic meiosis (since they do!) but envisioned this lineage as arising from ancestors with preexisting alternation of generations, for which there is no substantive evidence (only speculation), as I have discussed and will continue to discuss.

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