A Cytological Monograph of the American Species of Tradescantia

Abstract

1. Autopolyploidy, aneuploidy, segmental interchange, fragmentation, and differences in chromosome size were found in the nine genera and thirty-two species of the Commelinaceae which were investigated cytologically. 2. Chromosome pairing has been studied in five diploid species of Tradescantia. The average number of chiasmata per bivalent is found to be fairly constant for any one plant but varies widely from plant to plant, even within the same species. 3. Pollen sterility varies from 82 to 98 per cent among the diploid species and ranges from 71 to 89 per cent among the autotetraploids. 4. An extensive cytological survey of the species allied to T. virginiana shows them to be made up largely of (1) diploid races and species, mostly southern, and (2) autotetraploid races and species, mostly northern in distribution. 5. The autotetraploids have roughly twice the average radius of distribution of the diploids. 6. Terminal chiasmata and median attachment constrictions, conditions favoring autotetraploidy, ...