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.
Supporters of the homologous theory likely felt vindicated, even though Farmer and Digby cautioned that their results proved that no necessary correlation existed "between the periodic reduction in the number of the chromosomes and the alternation of generations .
The green alga Ulva replaced the brown alga Dictyota as the favored algal exemplar of the homologous theory (Graham, 1985; Blackwell, 2003) after Foyn (1929) and Hartmann (1929) described isomorphic alternation of generations in Ulva and Enteromorpha.
Therefore, land plants did not evolve from within any of the groups of algae in which extant members exhibit isomorphic alternation of generations.
Remy (1980), for example, argues that stoneworts evolved from an ancestor with isomorphic alternation of generations, but secondarily lost the diploid phase.
The total paleobotancial evidence, though, as previously discussed, does not support either theory of alternation of generations conclusively; put another way, the existing evidence could be argued to support both theories more or less equally.
A review of historical and recent opinions concerning alternation of generations in land plants has led to the conclusion that there still has been no clear decision (i.
The homologous theory of alternation of generations presents certain problems of logical content.