It is quite fitting that the nasturtium leaves should be shaped like shields, for that is one of their uses; they are shields to protect the young nasturtium seeds from the hot sun and from the view of devouring enemies. The nasturtiums are natives of Peru and Chili, and it is fitting that the leaves should develop in shield-shape, and the shields overlap until they form a tent to shade the tender developing fruit from the burning sun. But they were never meant to shield the flower, which thrusts its brilliant petals out between the shields, and calls loudly to the world to admire it. It would indeed be a pity for such a remarkable flower to remain hidden; its five sepals are united at their base, and the posterior one is extended into a long spur, a tube with a delectable nectar-well at its tip. The five petals are set around the mouth of this tube, the two upper ones differing in appearance and office from those below; these two stand up like a pair of fans, and on them are lines which converge; on the upper sepals are similar lines pointing toward the same interesting spot. And what do all these lines lead to, except a veritable treasure-cave filled with nectar! The lower petals tell another story; they stand out, making a platform, or doorstep, on which the visiting bee alights. But it requires a big insect to do the work of this flower, and what if some inefficient little bee or fly should alight on the petal-doorstep and steal into the cave surreptitiously! This contingency is guarded against thus: Each of these lower petals narrows to a mere insect footbridge at their inner end; and in order to render this footbridge quite impassable, it is beset with irregular little spikes and projecting fringes, sufficient to perplex or discourage any small insect from crawling that way.
But why all these guiding lines and guarded bridges? If you watch the same blossom for several successive days, it will reveal this secret. When a flower first opens, the stamens are all bent downward, but when an anther is ready to open its pollen doors, the filament lifts it up and places it like a sentinel blocking the doorway to the nectar treasure. Then when the robber comes, whether it be butterfly, bee or hummingbird, it gets a round of pollen ammunition for its daring. Perhaps there may be two or three anthers standing guard at the same time, but, as soon as their pollen is exhausted, they shrivel and give room for fresh anthers. Meanwhile, the stigma has its three lobes closed and lying idly behind and below the anthers; after all the pollen is shed, the style raises and takes its position at the cave entrance and opens up its stigmas, like a three-tined fork, to rake the pollen from any visiting insect, thus robbing the robber of precious gold-dust which shall fertilize the seeds in its three-lobed ovary. Although the flower needs to flare its colors wide to call the bees and hummingbirds, yet the growing seeds must be protected; therefore, the stem which held the flower up straight, now twists around in a spiral and draws the triplet seeds down behind the green shields.
Nasturtium leaves are very pretty, and are often used as subjects for decorative water-color drawings. The almost circular leaf has its stem attached below and a little at one side of the center; the leaves are brilliant green above but quite pale beneath, and are silvery when placed beneath the water. The succulent stems have a way of twisting half around the wires of the trellis and thus holding the plant secure to its support. But if there is no trellis, the main stem seems to awaken to the responsibility and grows quite stocky, often lifting the plant a foot or two in height, and from its summit sending out a fountain of leaf and flower stems.
The nasturtium is among the most interesting and beautiful of our garden flowers, and will thrive in any warm, sunny, fairly moist place. Its combinations of color are exceedingly rich and brilliant. H. H. says of it:
Leading thought—The nasturtium has a special arrangement by which it sends its own pollen to other flowers and receives pollen from other flowers by insect messengers.
Method—The nasturtiums and their foliage should be brought into the schoolroom in sufficient quantity so that each child may have a leaf and a flower for study. The object of the lesson is to interest the pupils in studying, in their gardens, one flower from the bud until the petals wither, taking note of what happens each day and keeping a list of the insect visitors.
1. Look at the back of the flower. What is there peculiar about the sepals? How many sepals are there? How many join to make the spur? What is in this spur? Taste of the tip. Find where the nectar is.
2. Look the flower in the face. How do the two upper petals differ in shape from the three lower ones? What markings are there on the upper petals? Where do these lines point? Are there any markings on the sepals pointing in the same direction? If an insect visiting a flower should follow these lines, where would it go?
3. Describe the shape of the lower petals. Suppose a little ant were on one of these petals and she tried to pass over to the nectar-tube or spur, would the fringes hinder her?
4. Look down the throat of the spur, and tell what a bee or other insect would have to crawl over before it could get at the nectar.
5. In your garden, or in the bouquet in the window if you cannot visit a garden, select a nasturtium that is just opening and watch it every day, making the following notes: When the blossom first opens where are the eight stamens? Are the unripe, closed anthers lifted so as to be in the path of the bee which is gathering nectar? How do the anthers open? How is the pollen held up in the path to the nectar? Can you see the stigma of this flower? Where is it? Note the same flower on successive days: How many anthers are open and shedding pollen to-day? Are they all in the same position as yesterday? What happens to the anthers which have shed their pollen?
6. When the stigma rises in the nectar path, how does it look? Where are all the anthers when the stigma raises its three tines to rake the pollen off the visiting insect? Do you know why it is an advantage to the nasturtium to develop its seed by the aid of the pollen from another plant?
7. Can you see the beginning of the seed-case when the stigma arises to receive the pollen?
8. The flowers project beyond the leaves. Do the ripening seed-cases do this? What happens to their stems to withdraw them behind the leaf?
9. Sketch a nasturtium leaf, and explain why it is like a shield. How does the leaf look when under water?
10. What sort of stem has the nasturtium? How does it manage to climb the trellis? If it has no trellis to climb, does it lie flat upon the ground?