ABSTRACT
There is very little experimental work which gives us any detailed understanding of the nature of the forces which act on and between chromosomes during the process of nuclear division; the nucleus is too carefully guarded within the cell to be easily reached by our present experimental methods. But the process of division, while remaining fundamentally the same throughout the biological realm, suffers in the different groups various modifications which can be regarded as natural experiments and these are numerous enough to enable cytologists to make deductions about the mechanisms involved. Particularly the study of meiosis in polyploids, which has been very vigorously pursued in recent years, has been found to provide crucial tests for many of the possibilities suggested by the phenomena in simpler forms. There is no space here to summarize the detailed evidence, which belongs to cytology proper rather than to genetics. However, a short account of the general conclusions arrived at must be given, since a knowledge of the forces between chromosomes obviously has a bearing on our idea of chromosome constitution.
