These red-purple and white flowers, which, massed in borders and beds, make gay our gardens and grounds in late summer and early autumn, have an interesting history. Professor L. H. Bailey uses it as an illustration in his thought-inspiring book, "The Survival of the Unlike;" he says that our modern petunias are a strange compound of two original species; the first one was found on the shores of the La Plata in South America and was introduced into Europe in 1823. "It is a plant of upright habit, thick sticky leaves and sticky stems, and very long-tubed white flowers which exhale a strong perfume at nightfall." The second species of petunia came from seeds sent from Argentina to the Glasgow Botanical Gardens in 1831. "This is a more compact plant than the other, with a decumbent base, narrower leaves and small, red-purple flowers which have a very broad or ventricose tube, scarcely twice longer than the slender calyx lobes." This plant was called Petunia violacea and it was easily hybridized with the white species; it is now, strangely enough, lost to cultivation, although the white species is found in some old gardens. The hybrids of these two species are the ancestors of our garden petunias, which show the purple-red and white of their progenitors. The petunias are of the Nightshade family and are kin to the potato, tomato, egg-plant, tobacco and Jimson-weed, and, like the latter, the flowers are especially adapted to give nectar to the long-tongued sphinx or hummingbird moths.
The petunia corolla is tubular, and the five lobes open out in salver-shape; each lobe is slightly notched at its middle, from which point a marked midrib extends to the base of the tube. In some varieties the edges of the lobes are ruffled. Within the throat of the tube may be seen a network of darker veins, and in some varieties this network spreads out over the corolla-lobes. Although many colors have been developed in petunias, the red-purple and white still predominate; when the two colors combine in one flower, the pattern may be symmetrical, but is often broken and blotchy.
When a flower-bud is nearly ready to open the long, bristly tube of the corolla lies with its narrow base set in the calyx, the long, fuzzy lobes of which flare out in bell-shape; the tube is marked by lengthwise lines made by the five midribs; the lobes of the corolla are folded along the outer portions of these midribs, and these folded tips are twisted together much as if some one had given them a half turn with the thumb and finger. It is a pleasing experience to watch one of these flowers unfold. When a flower first opens, there lies near the bottom of the throat of the tube the green stigma, with two anthers snuggled up in front of it and two behind it, the latter being not quite so advanced in age as the former. As the filaments of the front pair of anthers are longer than those of the rear pair, the little group lies at a low angle offering a dusty doormat for entering insects. If we open a flower at this stage, we find another anther, as yet unopened, and which is on the shortest stamen of the five. This seems to be a little pollen-reserve, perhaps for its own use later in the season. There is an interesting mechanism connected with these stamens; each is attached to the corolla-tube at the base for about half its length, and at the point of attachment curves suddenly inward so as to "cuddle up" to the pistil, the base of which is set in the nectar-well at the bottom of the flower. If we introduce a slender pencil or a toothpick into the flower-tube along the path which the moth's tongue must follow to reach the nectar, we can see that the stamens, pressing against it at the point where they curve inward, cause the anthers to move about so as to discharge their pollen upon it; and as the toothpick is withdrawn they close upon it cogently so that it carries off all the pollen with which it is brought in contact.
If we look at the stigma at the center of its anther-guard, it has a certain close-fisted appearance, although its outer edges may be dusted with the pollen; as the flower grows older, the stigma stands above the empty anthers at the throat of the flower tube and opens out into two distinct lobes. Even though it may have accepted some of its own pollen, it apparently opens up a new stigmatic surface for the pollen brought from other flowers by visiting insects.
Dr. James G. Needham says that at Lake Forest he has been attracted to the petunia beds in the twilight by the whirring of the wings of countless numbers of sphinx, or hummingbird moths which were visiting these flowers. We also may find these moths hovering over petunia beds in almost any region if we visit them on the warmer evenings. And it is a safe guess that the remote white ancestor of our petunias had some special species of sphinx moth which it depended upon for carrying its pollen; and the strong perfume it exhaled at nightfall was an odor signal to its moth friends to come and feast.
But even though the petunia flowers are especially adapted to the delectation of hummingbird moths, our bees which—like man—have claimed all the earth, will work industriously in the petunias, scrambling into the blossoms with much remonstrating, high-pitched buzzing because of the tight fit, and thus rifle the nectar-wells that were meant for insects of quite different build.
The leaves of the petunia are so broadly ovate as to be almost lozenge-shape, especially the lower ones; they are soft, and have prominent veins on the lower side; they are without stipules, and have short, flat petioles. The stems are soft and fuzzy and are usually decumbent at the base, except the central stems of a stool or clump which, though surrounded by kneeling sisters, seem to prefer to stand up straight.
The flower stems come off at the axils of the leaves, the lower flowers open first. The blossoms remain open about two days; at the first sign of fading, the lobes of the corolla droop dejectedly like a frill that has lost its starch, and finally the corolla—tube and all—drops off, leaving a little conical seed-capsule nestled snugly in the heart of the bell-shaped calyx. At this time, if this peaked cap of the seed-capsule be removed, the many seeds look like tiny white pearls set upon the fleshy, conical placenta. As the capsule ripens, it grows brown and glossy like glazed manila paper and it is nearly as thin; then it cracks precisely down its middle, and the seeds are spilled out at any stirring of the stems. The ripe seeds are dark brown, almost as fine as dust, and yet, when examined with a lens, they are seen to be exquisitely netted and pitted.
References—The Survival of the Unlike, L. H. Bailey; The Encyclopedia of Horticulture, Bailey; Our Garden Flowers, Harriet Keeler.
Leading thought—The petunias have an interesting history being native to South America. Their flowers are fitted by form and mechanism to entice the hummingbird moths as visitors, and to use them for carrying pollen.
Method—The petunias are such determined bloomers that they give us flowers up to the time of killing frosts, and they are therefore good material for nature lessons. Each pupil should have a flower in hand to observe during the lesson, and should also have access to a petunia bed for observations on the habits of the plant.
1. What colors do you find in the petunia flowers? If striped or otherwise marked, what are the colors? Are the markings symmetrical and regular?
2. Sketch or describe a flower, looking into it. What is the shape of the corolla-lobes? How many lobes are there? How are they veined? What peculiar markings are at the throat of the flower?
3. What are the color and position of the stigma? How are the stamens arranged? How many anthers do you see? What is the color of the anthers? Of the pollen?
4. Sketch or describe the flower from the side. What is the shape of the corolla-tube? Is it smooth or fuzzy? How is it marked? What are the number and shape of the sepals, or lobes, of the calyx?
5. Study a freshly opened flower, and describe the position and appearance of the anthers and stigma. Do they remain in these relative positions after the flower is old?
6. Cut open a flower, slitting it along the upper side. Describe the stamens and how they are attached. Is the pistil attached in the same manner? Where is the nectar? Thrust a slender pencil or a toothpick into the tube of a fresh flower. Does this spread the anthers apart and move them around? When it is withdrawn, is there pollen on it? Can you see in your open flower the mechanism by which the pollen is dusted on the object thrust into the flower?
7. What insects have tongues sufficiently long to reach the nectar-well at the bottom of the petunia flower? At what time do these insects fly? At what time of day do most of the petunia flowers open? Visit the petunia beds in the twilight, and note whether there are any insects visiting them. What insects do you find visiting these flowers during the day?
8. Sketch or describe the leaves of the petunia. How do the leaves feel? Look at a leaf with a lens and note the fringe of hair along its edges. Describe the veining of the leaf.
9. Describe the petunia stems. Are they stout or slender? How do they feel? With what are they covered? Where do the flower stems come off the main stalk?
10. Describe or sketch a flower-bud just ready to open. How are the tips of the lobes folded? How long does the flower remain in bloom? What is the first sign of its fading?
11. Describe the seed-capsule. Where does it open? Are the seeds many or few, large or small? What is their color when ripe? When examined with a lens, have they any pits or markings?