Germination of Hordeum vulgare at 35–36 °C. induced, in the nuclei of the root tips, numerous fractures in one or both chromatids, particularly in the attachment region of the chromosome. The fractured ends appeared to possess an unsatisfied attraction for each other. Chiasmata were formed by the union at random of the fractured ends which happened to lie close together in the nucleus, giving rise to associations of one and one-half, two, and three chromosomes involving chromatid interchange or crossing-over between non-homologous as well as homologous chromosomes. The manner in which fragmentation, translocation, and elimination of chromosome parts can occur in somatic tissue is demonstrated. Somatic segregation and the incidence of new linkage relationships are discussed.The formation of tetraploid and octaploid nuclei was induced in root tips of Pisum sativum by treatment with chloral hydrate. The chromosomes of these polyploid nuclei were frequently closely associated in pairs which bore a superficial resemblance to the paired associations observed in barley. The chromosomes, however, were never united by chiasmata and retained their juxtaposition solely through their inability to separate normally at anaphase.