The Effects of Ultraviolet and X-Ray Treatment on the Pollen Tube Chromosomes of Tradescantia.

HE cytogenetic interest in ultraviolet radiation resides in the hope T that the qualitatively discriminating nature of this type of radiant energy will yield still further evidence as to the structure and behavior of the hereditary mechanism. It is now known that ultraviolet, like X-rays, can produce gene mutations and chromosomal changes; it is likewise known that, unlike X-rays, ultraviolet is absorbed in a definite and specific manner by the proteins and nucleic acids which constitute, as far as we are aware, the physical basis of the gene. The integration of these two kinds of investigation, the one biological and the other physico-chemical, should, in time, yield a more informative mass of data concerning the relationship between absorption on the one hand and the genic or chromosomal change on the other than the less discriminating ionizing types of radiation. The difficulties encountered in securing and measuring the effective penetration of ultraviolet make it necessary to use a variety of organisms for genetical and cytological analyses. The studies of STADLER and SPRACUE (1936), STADLER (1939), and MULLER and MACKENSIE (1939) have been on effects visible only after the course of many cell generations, and on those which in diploid cells are genetically viable and hence transmissible. It has been shown that such studies can be confirmed and furthered by an analysis of the more immediate effects of ultraviolet through use of the pollen tube technique (SWANSON 194oa, b), which permits an analysis of both viable and non-viable chromosomal changes before they can be eliminated through the processes of mitotic division.