petals begin to expand, the five stamens opposite the sepals
lengthen in about two hours, and by sunset the anthers, which
have matured at the same time, are covered with pollen. So they
remain until the forenoon of the second day, and then the emptied
anthers hang like shriveled bags, or drop off altogether. Late in
the second afternoon, the second set of stamens repeat the
actions of their predecessors, bend backward and shed their
anthers the following, that is to say the third, morning. But on
the third afternoon up rise the S-shaped, twisted stigmas, which
until now had been hidden in the center of the flower. Moths,
therefore, must transfer pollen from younger to older blossoms.

"With this lengthening and bending of the stamens and stigmas,"
says Dr. Kerner, "goes hand in hand the opening and shutting of
the corolla. With the approach of dusk, the bifid limbs of the
petals spread out in a flat surface and fall back against the
calyx. In this position they remain through the night, and not
till the following morning do they begin (more quickly in
sunshine and with a mild temperature, more slowly with a cloudy
sky and in cold, wet weather) to curl themselves up in an
in-curved spire, while at the same time they form longitudinal
creases, and look as though they were gathered in, or
wrinkled;...but no sooner does evening return than the wrinkles
disappear, the petals become smooth, uncurl themselves, and fall
back upon the calyx, and the corolla is again expanded."

Curiously enough, these flowers, which by day we should certainly
say were not fragrant, give forth a strong perfume at evening the
better to guide moths to their feast. From eight in the evening
until three in the morning the fragrance is especially strong.