1. Comparisons were made of DNA content per nucleus in common wheat, artificially synthesized 6x wheat, its parental species and three analyzers.
2. DNA content per nucleus in the D genome analyzer was the lowest, B genome had a little lower DNA content than A genome, but the difference between the last two was not significant.
3. Ssp. strangulata had a significantly higher DNA value than var. typica of the same species, Ae. squarrosa.
4. Two strains of synthesized 6x wheat, ABD No. 1 and ABD No. 13, have nuclear DNA equal to the sum of the DNA contents of their respective parents. Nuclear DNA content of cultivated common wheat (Chinese Spring) is quite the same as that of synthesized 6x wheat, especially ABD No. 13.
5. In three subspecies of T. aestivum, vulgare, spelta and macha no significant difference was found in DNA content per nucleus.
6. Based on the above facts, the following conclusion may be reasonably drawn as far as wheat and its relatives are concerned:
a) Appreciable changes of DNA content might have resulted from chromosome aberrations accumulated in the course of genome differentiation of a common primitive genome at the diploid level.
b) The three different genomes, once established, have been appreciably stable and kept the amount of DNA constant either in diploid or polyploid condition.