Abstract
A new haploid Oenothera, derived by parthenogenesis from the diploid form as a result of cross-pollination of a flower of the diploid, has been described with special reference to its meiosis. The diploid (Oe. blandina) is homozygous, having seven pairs of chromosomes. The haploid plant shows seven univalents in 80% of the pollen mothercells, and various bivalent, trivalent and quadrivalent configurations of chromosomes in the renaining 20% of cells. Corresponding multivalents have been seen in the diploid. The associations of chromosomes in the haploid prove the presence of reduplicated segments in the chromosome complement. In one case, the reduplicated segment is terminal in one chromesome and interstitial in the other. The unequal configuration produced proves that chiasma formation is associated with and is a direct result of cytological crossing-over; such a configuration would lead to reduplication of end segments.
The significance of the reduplications in relation to segmental interchange, translocation and the origin of a self-perpetuating ringmechanism is discussed. Proofs of various other principles are given, including (i) the random segregation of chromosomes at anaphase I in the haploid, (ii) the disturbance in the random distribution caused by lagging of chromosomes and subsequent formation of restitution nuclei, (iii) terminalisation of chiasmata in the diploid, (iv) random occurrence of chiasma failure in the diploid. The arrest of terminalisation, due to a change in the linearr homologies of the chromosomes, is clearly established by the pairing phenomena in the haploid.
