Published online by Cambridge University Press: 14 April 2009
1. Chromosome 6B of T. aestivum, to which a small segment of an Ae. umbellulata chromosome had been translocated, was examined both by interference microscopy and in stained preparations.
2. In the stained preparation a constriction was observed in the long arm of chromosome 6B and also a terminal knob that was also observed on chromosome A of Ae. umbellulata.
3. These features were also observed by interference microscopy and in addition the portion of the chromosome 6B of Transfer distal to the constriction had different phase-retarding properties.
4. It is concluded that the part of chromosome 6B distal to the constriction is the part of Ae. umbellulata chromosome A which carries the gene for the leaf-rust resistance of that species and of the wheat variety into which it was translocated.