When, through radiation or other causes, chromosomes are broken within a single nucleus, 2-by-2 fusions may occur between the broken ends. These fusionsmay lead to rearrangements of parts of the chromatin com-plement, giving rise to variouschrorrosomal aberrations which are detected as reciprocal translocations, inversions, deficiencies, etc. Since, in the well-investigated cases, the breakages occurred within a single nucleus, the conditions that lead to fusions of broken ends could not easily be ascertained. The following questions have been asked:(1) Must two or more chromosomes be in intimate contact at the time of breakage in order that fusions may occur?(2) If no intimate contact is necessary at the time of breakage, are the broken ends" unsaturated," that is, capable of fusion with any other unsaturated broken end?(3) If question (2) can be answered in the affirmative, what forces are involved which lead to the contact and subsequent fusions of the two unsaturated broken ends? Likewise,(4) how long will these broken ends remain unsaturated, ie, capable of fusion?

Questions (1) and (2) could be answered if the following conditions were present: Assume that fusion occurs between two nuclei each of which possesses one chromosome, one end of which has been broken. Each nucleus will then have a single broken end. When these nuclei fuse and their chromosomes intermix within a single nucleus, the chromosome with a broken end contributed by one nucleus could fuse with the chromosome with a broken end contributed by the second nucleus. The chromosome fusion should occur between these two broken ends. This experiment may easily be conducted in maize. The two nuclei that fuse can be the male and the female gametes, respectively. The method of obtaining