In oder to consider the phylogeny of wheat and its relatives, nuclear DNA content in 43 strains belonging to section Sitopsis of the genus Aegilops was measured Feulgen-cytophotometrically using pollen tetrad nuclei.
1) Forty three strains showed a graded series of DNA content from the lowest of 180 to the highest of 314, that is, variation of 1.74 fold between both extremes.
2) Significant difference in nuclear DNA content among five taxa were observed and were formulated as follows, sharonensis>longissima=bicornis>speltoides=aucheri.
3) Test of significance on the mean difference between species revealed no difference between Ae. speltoides and Ae. aucheri which are very close relatives with one another.
4) There are intraspecific variations in two species with S¹ genome, Ae. longissima and Ae. sharonensis. But Ae. speltoides (S genome) and Ae. aucheri (S) and Ae. bicornis (S^b) had no significant variation within species.
5) Species relationships in section Sitopsis of the genus Aegilops were discussed.