Chromosome numbers of different species of Prunus have been investigated. Usual diploid chromosome number of these plants is 16, but three species in the subgenus Padus have been proved to be tetraploid (32). Further more it is remarkable that about one-third of 30 double flowered garden varieties of Japanese cherry trees (P. serrulata LINDL.) show triploid chromosomes (24) in somatic divisions. In the first nuclear division in the pollen-mother-cells of these triploid plants appear usually 8 trivalent chromosomes.