Spontaneous Chromosome Aberrations in Triploid Tradescantia Hybrids.

T HAS recently been found that chromosome aberrations of the types I induced by various kinds of radiations occur spontaneously during the development of the pollen grains in diploid species and especially in species hybrids of Tradescantia (GILES 1940). The present studies have shown that the frequency of these aberrations is even higher in triploid Tradescantia hybrids. Furthermore, it has been found that another class of aberrations is also present at mitosis in the pollen grains of the polyploids-those types resulting from chromosome behavior at meiosis. To aid in interpreting and distinguishing this latter class of aberrations, rather extensive observations of meiotic chromosome behavior were made, and these have already been reported in an earlier study (GILES 1941). The present paper will discuss the types and frequencies of aberrations at the first post-meiotic mitosis in the pollen grains of the triploid hybrids and in their diploid and tetraploid parents. Certain observations of aberrations in the somatic (root-tip) mitoses of these plants will also be reported. The plants used in this investigation were a diploid Tradescantia paludosa Anders. & Woodson (2X = 12), an autotetraploid T . canaliculata Raf. (& = 24), and several triploid hybrids (all 3X = IS) resulting from a cross of these two individuals, the diploid being used as the female parent. A further discussion of the plants used is given in the paper previously mentioned (GILES 1941). Aceto-carmine smears were used to study the pollen grain mitoses, and Feulgen smears for the root-tip mitoses.