The most familiar nocturnal wild-flower east of the Alleghanies is the evening primrose (CEnothera biennis) (Fig. 58). It is extremely common everywhere in the Northern Atlantic states - along roadsides, in fence corners, and around the edges of thickets. By day its appearance is uninteresting. A stalk from three to six feet tall bears a profusion of long, narrow, rather coarse leaves, and above them a spire of faded flowers and buds. In the afternoon the primrose has nothing to show but fading flowers and buds, and one is reminded of "jam yesterday and jam to-morrow - but never jam to-day,"in "Alice in Wonderland." The faded blossoms bloomed the night before last, the wilting ones were beautiful last night, the large buds above them will expand this evening. About sunset or a little sooner, if the plant is in the shade, they begin to swell. The green calyx splits in four places, disclosing four lines of gold which widen under our eyes. Then, with a start and a jerk, one narrow sepal draws backward, and the yellow corella is revealed. Little thrills go through the bud, like the slight movement of an awakening child. A second sepal draws backward, and then a third, and with an impulse of fully-aroused life the flower bursts its last bond and opens wide, showing its heart of gold. A delicate perfume is shed abroad; and by this as well as by the gleam of yellow petals the moth is lured to the flower.
There is a garden evening-primrose which opens in a most impressive manner, with a sudden flare of golden petals, and a slight pop, like that made by withdrawing a small but stubborn cork. But the wild evening-primroses open slowly, with little pauses and delays, as if they were half afraid to venture into the untried life before them.
Along the Ohio valley and in the alluvial country westward (and in many places further east) the commonest night-flower is the Jamestown or jimson-weed (Datura stramonium) (Fig. 59). The vagabond habits of this dweller in waste ground, its rank, weedy aspect, and the disagreeable smell of its leaves, spoil the impression which might be made by the beauty of the blossoms were they not so lowly born. Growing with the jimson-weed we may find its first cousin, the Datura tatula, a smaller plant bearing flowers strongly tinged with purple. The buds of both species expand late in the afternoon - from four to six o'clock, according to the weather. Both are immigrants from warmer lands, but it is evident that they have made friends among the native night-flying insects, for the thorny seed-vessels follow duly upon the fading of the flowers.
Fig. 58. - A wild evening primrose (CEnothera biennis).
Fig. 59. - Jimson-weed (Datura stramonium).
The night visitor of the jimson-weed is the Sphinx Carolina (Fig. 60), a large moth whose caterpillar has a great and evil reputation throughout the South, where it is known as the "tobacco-worm." In our gardens these caterpillars live on the tomato-vines. They are large, but it is difficult to see them, notwithstanding, as their bodies are of exactly the same tint as the vinestems. The full-grown moths appear in June, and on any warm, clear evening, from midsummer till frost, they may be seen, hovering like hummingbirds above the blossoms of their choice.
Fig. 60. - Night visitor to the jimson-weed (Sphinx Carolina).
(From Harris' Insects Injurious to Vegetation).
Fig. 61. - Hedge bind-vveed (Convolvulus sepium).
"The flowers of the great convolvulus (Fig. 61) or hedge bind-weed close," says Muller, "on cloudy evenings" - but on moonlight nights they are all wide awake, and watching for their best friend, the Sphinx convolvuli. In England, where this great night-moth is rare, the hedge bind-weed seldom produces seed, though it may be visited and fertilized in the morning hours by the sunshine-loving butterflies.
But in our warm summer twilights Sphinx convolvuli is not uncommon, and one may catch him, as he has been caught aforetime, by a naturalist who "stood by a moonlit hedge, overgrown with convolvulus, held thumb and finger over a flower, and closed its orifice when the moth had entered".
The pretty roadside saponaria, familiarly known as "bouncing Bet," expands about sundown, and in the twilight its sweets are sipped by sphinx-moths, which, doubtless, help to transfer its pollen. It remains open throughout the following day and entertains butterflies; but the strong fragrance of the flowers at evening shows that night-moths are the favorite guests. The stamens of the bouncing Bet are ten in number. Soon after the flower opens five of them thrust their heads out of the tube, and their anthers ripen and split. When they have shed their pollen, the other five emerge, mature, and open.
All this time the young pistil lies concealed in the flower-tube, but, after the second quintette of stamens have given away most of their store, it comes out of its seclusion, and the two long stigmas expand themselves. The butterfly guests by day and the moth visitors by night carry pollen from the stamens of younger flowers to the pistils of older ones.
Many members of the pink family, to which "bouncing Bet" belongs, have formed the habit of ripening two successive quintettes of stamens, and, last of all, the pistil. This arrangement makes sure that the flower will set seed only by aid of pollen brought from another, and that its seeds (if they are formed) will be endowed with great vitality. But the family is placed entirely at the mercy of flying insects, for without their ministrations no seed can be set at all. So the whole future of such flower families depends upon the success with which its members entice their winged friends.