Abstract

Seeds of S. purpureo-sericeum irradiated with dosages of thermal neutrons 3.5x10 n/cm2 or 4.0x10 n/cm2 at the flux intensity of 3.2 x 10 n/cm2 sec. showed no marked decrease in seed viability, but These treatments caused an appreciable reduction in seedling height and plant tillering. At the Same total dosage of thermal neutrons 3.5x 10 n/cm2， if the flux was increased from 3.2xl0 n/cm2 sec. 10 6.54x 10 n/cm sec., caused all the treated seeds 10 die. It showed that the flux was more effective in damaging seed viability than the total dosage of thermal neutrons In the present study, we learn that the exposure of 4.0x10 n/cm2 at a constant intensity of flux 3.7 x10 n/cm2 sec. is the better one for Thermal neutron treatment as this yields the most aberrations and at which the large numbers of types of chromosome aberrations were induced. Most of them were a ring., or chain-of-four and the next most common aberration was pseudo-isoehromosomes. The application of Koo's expression, the Theoretical ratio of rings and pseudo-isochromosomcs ln S. purpureo-sericeum was obtained. Results from the comparisons of observed data for S. purpureo-sericeum with the theoretical ratio indicates that the interchange between chromosomes homolologous or nonhomologous were random. From the information shown in this experiment , we know that the frequency of multivalent may be independent of the zigzag frequency in a translocation heterozygote, while the frequency of multivalent is proportional 10 the percentage of chromosome non-disjuction in a translocation heterozygote. Three kinds of chlorophyll mutations were found among the plants grown from seeds irradiated with thermal neutrons. Of a total 18 mutants, half of them were white, 38.89% were light green and 11% were iojap.