Abstract
In the F1 hybrids of Paraixeris denticulata×Crepidiastrum Keiskeanum, some of the paternal chromosomes undergo fragmentation and some fragments are eliminated; hence a difinite karyotype cannot be determined. This phenomenon is assumed to be caused by disturbance in the chromosomal duplication of the paternal chromosomes within the foreign cytoplasm of the maternal cell. To acertain the cause, in one experiment, an excess of RNA was given to just fertilized egg cell. The process is: after the fertilization, flower heads were wrapped with cotten pieces immersed in RNA solution and the cotten was left on the flower for 4 days with occasional addition of RNA solution. The mature achenes thus obtained were examined whether they yield plants somewhat different from the control. Three hybrids obtained from the treated flowers showed practically no fragmentation of chromosomes and no aberrant cells, while the hybrids from the flowers in which RNA application was delayed for 24 hours showed abnormalities which are common with the control. From these results it is assumed that the excess of RNA in the fertilized cell may act as a curing agent of the chromosome fragmentation.
