1) Corresponding taxa are known to include two kinds of plants, true vicariads, which have penetrated into a new area and later become differentiated, and false vicariads or substitution taxa, which have differentiated prior to their occupation of new areas. It is pointed out that although this geobotanical definition does not fully agree with the present grouping of species into gradual-species and abrupt-species, the latter never are vicarious, while perhaps the majority of the former are true vicariads. 2) By aid of cytotaxonomical studies it is shown that, within all groups of corresponding taxa, vicarious as well as substitution types are met with. This is shown to be true at the initial stage of habitat separation in the same region, in montane localities as compared with lowland habitats, as well as in regions separated by other physiographic and historical barriers. 3) A number of corresponding types from North America and Europe are compared from this point of view. It is demonstrated that while 92 pairs of taxa are truly vicarious in both regions, as many as 41 pairs are substitution species, differing in the number of chromosomes. A number of insufficiently known pairs are also listed. 4) It is pointed out that while cytotaxonomy might be of great help to geobotany in separating groups of different significance, these two branches of botany connected with modern taxonomy are in urgent need of much closer cooperation in order to solve many problems of evolutionary importance.
- 1 - sciences appliquees, technologies et medecines
- 2 - sciences biologiques et medicales
- 3 - sciences biologiques fondamentales et appliquees. psychologie
- 1 - Life Sciences ; 2 - Agricultural and Biological Sciences ; 3 - Plant Science
- 1 - Physical Sciences ; 2 - Environmental Science ; 3 - Ecology