The Sweet Pea
MONG the most attractive of the seeds which make up the treasure of the children's seed packets, the sweet peas are of the prettiest. They are smooth, little white or brown globules, marked with a scar on the side, showing where they were attached to the pod. One of these peas divides readily into two sections; and after it has been soaked in water for twenty-four hours, the germ of the future plant may, with the aid of a lens, be seen within it. After planting, the sprout pushes through the seed-coat at a point very near the scar, and leaf shoots emerge from the same place; but the two act very differently. The leaf lifts upward toward the light, and the root plunges down into the soil. As the plant grows, it absorbs the food stored in the seed; but the seed remains below ground and does not lift itself into the air, as happens with the bean. The root forms many slender branches, near the tips of which may be seen the fringe of feeding roots, which take up the food and water from the soil. The first leaves of the pea seedling put forth no tendrils, but otherwise look like the later ones. The leaves grow alternately on the stalk, and they are compound, each having from three to seven leaflets. The petiole is winged, as is also the stem of the plant. There is a pair of large, clasping stipules at the base of each leaf. If we compare one of these leaves with a spray of tendrils, we can see that they resemble each other in the following points: The basal leaflets of the petiole are similar and the stipules are present in each case; but the leaflets nearest the tip are marvelously changed to little, stiff stems with a quirl at the tip of each ready to reach out and hook upon any object that offers surface to cling to. Sometimes we find a leaflet paired with a tendril. The sweet pea could not thrive without a support outside of itself.
Of course, the great upper petal of the sweet pea blossom is called the banner! It stands aloft and proclaims the sweet pea as open; but before this occurs, it tenderly enfolds all the inner part of the flower in the unopened bud, and when the flower fades it again performs this duty. The wings are also well named; for these two petals which hang like a peaked roof above the keel, seem like wings just ready to open in flight. The two lower petals are sewed together in one of Nature's invisible seams, making a long, curved treasure chest resembling the keel of a boat, and it has thus been called. Within the keel are hidden the pistil and stamens. The ovary is long, pod-shaped and downy; from its tip the style projects, as strong as a wire, curving upwards, and covered with a brush of fine, white hairs; at the very tip of the style, and often projecting slightly from the keel, is the stigma. Around the sides and below the ovary and style, are nine stamens, their filaments broadening and uniting to make a white, silken tube about the ovary, or young pod. From the tip of this stamen-tube, each of the nine filaments disengages itself, and lying close to the style thrusts its anther up into the point of the keel, below the stigma. But strange to say, one lone, lorn stamen "flocks by itself" above the pistil, curving its anther up stigma-ward. If we touch the point of the keel with the finger, up fly—like a jack-in-the-box—the anthers splashing the finger with pollen; and if a bee, in her search for nectar, alights on the wings at the very base of the petals, up flies the pollen brush and daubs her with the yellow dust, which she may deposit on the stigma of another flower. The interesting part of this mechanism is the brush near the tip of the style below the stigma—a veritable broom, with splints all directed upward. As the pollen is discharged around it, the brush lifts it up when the keel is pressed down, and the stiff petals forming the keel, in springing back to place, scrape off the pollen and plaster it upon the visitor. But for all this elaborate mechanism, sweet peas, of all flowers are the most difficult to cross-pollenate, since they are so likely to receive some of their own pollen during this process.
The sweet-pea bud droops, a tubular calyx with its five-pointed lobes forming a bell to protect it. Within the bud the banner petal clasps all in its protecting embrace.
After the petals fall, the young pod stands out from the calyx, the five lobes of which are recurved and remain until the pod is well grown. As the sweet pea ripens, all the moisture is lost and the pod becomes dry and hard; through the dampness of dews at night and the sun's heat which warps it by day, finally each side of the pod suddenly coils into a spiral, flinging the seed many feet distant in different directions.
The Sweet Pea
Leading thought—The sweet pea has its leaflets changed to tendrils, which hold it to the trellis. Its flower is like that of the clover, the upper petal forming the banner, the two side petals the wings, and the two united lower petals the keel which protects the stamens and pistil.
Method—This should be a garden lesson. A study should be made of the peas before they are planted, and their germination carefully watched. Later, the method of climbing, the flower and the fruit should each be the subject of a lesson.
Observations on germination—
1. Soak some sweet peas over night; split them the next morning. Can you see the little plant within?
2. Plant some of the soaked peas in cotton batting, which may be kept moist. At what point does the sprout break through the seed covering? Do the root and leaf-shoot emerge at the same place, or at different points? Which is the first to appear?
3. Plant some of the soaked peas in the garden. How do the young plants look when they first appear? Does the fleshy part of the seed remain a part of the plant and appear above the ground, as is the case with the bean? What becomes of the meat of the seed after growth has started?
4. Do the first leaves which unfold from the seed pea look like the later ones? Are the leaves simple or compound? Do they grow opposite each other or alternately?
5. Take a leaf and also a spray of the tendrils. How many leaflets are there in a compound leaf? Describe the petiole and the basal leaves. How far apart are the leaflets on the mid-stem? Compare the stem on which the tendrils grow with this leaf. Are the basal leaflets like those of the leaf? Is the petiole like that of the leaf? Do you think that the leaflets toward the tip of the stem often change to tendrils? Why do you think so? Why must the sweet pea have tendrils? Do you see the earlike stipules at the base of the leaf? Are there similar stipules at the base of the tendril stem?
Observations on the flower and fruit—
1. Take the sweet pea in blossom. Why is the large upper petal called the banner? How does it compare in size with the other petals? What is its purpose when the flower is open? Why do you think the side petals are called wings? What is their position when the flower is open?
2. Describe that part of the flower below the wings. Do you think that it is made of two petals grown together? Why is it called the keel of the flower? Press down with your finger on the tip of the keel. What happens? Is your finger splashed with pollen? Where is the nectar in the sweet pea? Would an insect getting the nectar press down upon the keel and receive a splash of pollen?
3. Open the keel. How many stamens do you find within it? How many have their filaments joined together? Is there one separate from the others? Against what are the anthers pressed by the keel?
4. Remove the stamens and describe the pistil. Which part of this will make the pod in which the new peas will develop? Describe how the style is curved. How is the style covered near its tip? What is this brush for? Can you find the stigma with the help of the lens? When the bee is seeking for nectar and pushes down on the keel, does the stigma push out at the same point as the pollen? Does this enable the stigma sometimes to receive pollen which the bees bring from other flowers?
5. Describe an unopened flower bud. What is its position? How many lobes to the calyx? What is their shape, and how do they protect the bud? Which petal is folded over all the others? How does the position of the open flower differ from that of the bud?
6. How does the young pod look when the petals fall? How does it look when ripe? How does it open to scatter little, ripe sweet peas? Do the lobes of the sepals still remain with the pod?