_Oenothera biennis_
_Flowers_--Yellow, fragrant, opening at evening, 1 to 2 in. across,
borne in terminal leafy-bracted spikes. Calyx tube slender, elongated,
gradually enlarged at throat, the 4-pointed lobes bent backward; corolla
of 4 spreading petals; 8 stamens; 1 pistil; the stigma 4-cleft. _Stem:_
Erect, wand-like, or branched, 1 to 5 ft. tall, rarely higher, leafy.
_Leaves:_ Alternate, lance-shaped, mostly seated on stem, entire, or
obscurely toothed.
_Preferred Habitat_--Roadsides, dry fields, thickets, fence-corners.
_Flowering Season_--June-October.
_Distribution_--Labrador to the Gulf of Mexico, west to the Rocky
Mountains.
Like a ball-room beauty, the Evening Primrose has a jaded, bedraggled
appearance by day when we meet it by the dusty roadside, its erect buds,
fading flowers from last night’s revelry, wilted ones of previous
dissipations, and hairy oblong capsules, all crowded together among the
willow-like leaves at the top of the rank-growing plant. But at sunset a
bud begins to expand its delicate petals slowly, timidly--not suddenly
and with a pop, as the evening primrose of the garden does.
Now, its fragrance, that has been only faintly perceptible during the
day, becomes increasingly powerful. Why these blandishments at such an
hour? Because at dusk, when sphinx moths, large and small, begin to fly,
the primrose’s special benefactors are abroad. All these moths, whose
length of tongue has kept pace with the development of the tubes of
certain white and yellow flowers dependent on their ministrations, find
such glowing like miniature moons for their special benefit, when
blossoms of other hues have melted into the deepening darkness. If such
have fragrance, they prepare to shed it now. Nectar is secreted in tubes
so deep and slender that none but the moths’ long tongues can drain the
last drop. An exquisite, little, rose-pink twilight flyer, his wings
bordered with yellow, flutters in ecstasy above the Evening Primrose’s
freshly opened flowers, transferring in his rapid flight some of their
abundant, sticky pollen that hangs like a necklace from the outstretched
filaments. By day one may occasionally find a little fellow asleep in a
wilted blossom, which serves him as a tent, under whose flaps the
brightest bird eye rarely detects a dinner. After a single night’s
dissipation the corolla wilts, hangs a while, then drops from the
maturing capsule as if severed with a sharp knife. Few flowers,
sometimes only one opens on a spike on a given evening--a plan to
increase the chances of cross-fertilization between distinct plants; but
there is a very long succession of bloom. If a flower has not been
pollenized during the night it remains open a while in the morning.
Bumblebees now hurry in, and an occasional humming bird takes a sip of
nectar. Toward the end of summer, when so much seed has been set that
the flower can afford to be generous, it distinctly changes its habit
and keeps open house all day.