Abstract
The quadrivalents formed by an autotetraploid Avena are of all the ten possible types. The equilibrium positions of their chiasmata are influenced by the spindle-attachment repulsions of chromosomes not taking part in them. The axial orientation of two members of a quadrivalent can be suppressed by that of the other two owing to the rigidity of the chromatids at an interstitial chiasma between the first two. These observations bear out the mechanical principles inferred from simpler configurations.
I am indebted to Professor Kihara for kindly providing me with the facilities for undertaking this study in his department at the Biological Institute, Kyoto Imperial University.
