GENETICS: B. P. SONNENBLICK cleus opposite the chromosomes are very interesting, but of questionable significance. If, as Cleveland asserts (op. cit., also, Science, 81, 598 (1935)), all of these fibres are merely astral rays, then it is not surprising that they are visible in the living organism. Moreover, the homology of such a bizarre achromatic apparatus with that of multicellular organisms is by no means clear.

GENETICS: B. P. SONNENBLICK in only chromatid aberrations including a considerable number of simple chromatid deletions and occasional chromatid exchanges Ultra-violet radiation of the generative nucleus in the pollen tube induces only simple chromatid deletions. The loss of only one of the two chromatids is in accord with the genetic observations that ultra-violet radiation produces primarily fractional endosperm deficiencies in maize. No configurations representing an interchange of chromatin between non-homologous chromosomes were found.The qualitative difference between the types of breaks induced by x-ray and ultra-violet radiation is tentatively explained by assuming that the sphere of influence of a single x-ray quantum is much greater in area than that of a single ultra-violet quantum. The vast difference in energy values, and the difference in the physical behavior attendant to absorption of the respective quanta supply a possible physical and chemical basis for this variation in degree of effectiveness.

No abstract

No abstract