1. The inflorescence of the oak has been evolved through a serial reduction of the panicle as is presented in the figure 1. 2. Perianth lobes though they range from one to twelve in a flower six loves occur more than 50% of tested flowers as is tabulated in the table 1. They have been increased partly by a fusion of flowers and partly by a reversion of the stamen into the perianth lobe. They also have been decreased by a fusion of perianth lobes each other. 3. Stamen numbers in a flower range from one to twenty four, but eight stamens are more common than the others as is shown in the table 1. They have been increased by a fusion of flowers and decreased by a fusion of stamens in a flower as are presented in the figure 4. 4. Floral position in the inflorescence, environmental factors, hybridity, and abnormal nutrition supply seem to accelerate fusion and reduction of the stamen in a flower. 5. Flowers which consist of eight stamens and six perianth lobes occur more common than the others, however, the number of the stamen (Y) and the perianth lobes (X) appear to be correlated as follows (see also fig.5.). Y=1.09X+3.78, r=0.4 for Q. dentate Thumb. (7004 flowers investigated) Y=0.71X+4.18, r=0.48 for Q. mongolica Fischer (7409 flowers investigated) Y=1.03X+2.91, r=0.4 for Q. allena B1. (8662 flowers investigated) Y=0.69X+2.00, r=0.4 for Q. serrata Thumb. (9048 flowers investigated) 6. Morphological similarity of the bracteoles and perianth lobes as illustrated in the fig. 3, phenomena of a fusion of bracteoles and separation of perianth lobes into three groups in a flower, and increasing and decreasing phenomena of the stamen number and perianth lobes in a flower as presented in the figures 3 and 4 support the proposal on the oak flower evolution made by H. Hjelmquist in 1948.