Lesson CLVII

The Nasturtium

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.

Observations—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?