1. To understand the mechanism of flower colour variations from red to
purple in crape myrtle cultivars, absorption spectra and Hunter's L,
a, b values of intact petals were measured. In this study 67 cyanic pl
ants were classified into two groups : red group, lambda(max1), 524 si
milar to 544 nm; b/a, (-0.183) similar to (+0.165) : purple group, lam
bda(max1) 555 similar to 570 nm; b/a, (-0.785)similar to(-0.442). Rela
tively strong absorption about 360 nm was recognized in purple flowers
, and high negative correlation (r=-0.897**) was obtained between b/a
and E(360)/E(VIS max). 2. Three anthocyanins from the red and purple
flowers were isolated, analysed chromatographically and spectrally, an
d their ratios determined. All 67 plants contained the 3-glucosides of
delphinidin, petunidin, and malvidin as the major anthocyanins. The r
atios among these anthocyanins varied widely, but had no correlation t
o Hue values (b/a), except that in the red group there was a negative
correlation between b/a and the relative malvidin 3-glucoside concentr
ation, and a positive one between b/a and relative delphinidin 3-gluco
side cone. 3. The pH values measured by tightly pressing the petals to
a flat electrode varied from 4.2 to 5.1, but there was no correlation
between these values and flower colour. 4. Crude aqueous extracts fro
m the red and purple flowers were partitioned with ethyl acetate and t
he organic fraction was concentrated; the aqueous fraction was dissolv
ed in a buffer solution. Visible absorption maxima shifted bathochromi
cally when the above two fractions from red and purple flowers were co
mbined. 5. Ellagic acid derivatives detected in the purple flowers are
assumed to be the main agents for the blueing of the flowers in crape
myrtle.