parison of the idiograms of the three species (Plate LX) 
reveals that, except for the nucleolus organizing chromo- 
some, the chromosomes of the three species are quite 
dissimilar in their morphology. The length of each 
chromosome, its arm ratio, and the contribution its 
length made to the total length of the genome are given 
for the three species in Table II. C. aquatica has the 
longest chromosomes of the complement, with a genome 
which is 401.9% long (mean chromosome length of 
80.38). The genomes of C. Lachryma-Jobi and C. gig- 
antea respectively are 582.0% (mean chromosome length 
of 58.24) and 488.84 (mean chromosome length of 
54.31) long; thus C. Lachryma-Jobi and C. gigantea 
have genomes of approximately equal length. They are 
also shorter than that of C. aquatica by about 40%. The 
nucleolus organizing chromosomes of the three species, 
even though of widely differing lengths and arm-ratios, 
are similar: they are median to submedian, and the nu- 
cleolus organizer occupies a sub-terminal position. The 
dissimilar morphology of chromosomes between the pre- 
sumably basic diploid C. aquatica and the derived poly- 
ploid species C. Lachryma-Jobi and C. gigantea must 
reflect, on the one hand, the effects of hybridity and 
chromosome doubling which presumably have been in- 
volved in the emergence of the species with higher chro- 
mosome numbers, and, on the other hand, the proneness 
of the genome of C. aquatica to re-patterning due to 
translocation (Venkateswarlu and Chaganti, 1973). Inter- 
specific hybrids between C. aquatica and C. Lachryma- 
Joli, C. Lachryma-Jobiand C. gigantea, and C. aquatica 
and C. gigantea are feasible, and the chromosomes in the 
I’, hybrids exhibit intergenomic pairing (unpublished ob- 
servations of Rao). Thus, at least one genome is common 
to all three species even though its presence cannot be de- 
tected by comparison of chromosome morphology alone. 
[ 216 ] 
