Abstract:18-26S rDNA loci were mapped on chromosomes in four species of Par
is，and the num-ber and position of rDNA sites in these species were compared f
or analysis of the distribution of the sites. All the plants were diploids，and t
he genome consisted of five chromosomes，A，B，C，D and E. （1）P. polyphylla var.
yunnanensis，2n=10=6m+4t. Two18-26S rDNA loci were de-tected on the short arms o
f C and D chromosomes;（2）P. forrestii，2n=10=6m+4t. One locus was detected on th
e long arm of B chromosome，and also two loci on the short arms of C and D chro-
mosomes;（3）P. axialis. 2n=10=6m（2sat）+4t（2sat）+1-2B. Two loci were detected o
n the short arms of C and D chromosomes. One locus was detected in the cell with t
wo B-chromosomes（B），but none was detected in that with only one B chromosome，
indicating that rRNA gene existed on B chromsome，and an unequal division occurr
ed during mitotic cycle of B-chromosomes. （4）P. daliensis，2n=10=4m+2sm+2st+2t. O
ne locus was detected on the short arm of D chromo-some. The signals of18-26S rD
NA appeared not only in the second constriction but also in the other regions of
chromosome. It is noteworthy that one locus was detected in the terminal region o
n the short arm of C chromosome in all the four species studied.