Lesson CXXXIII

Pondweed

Leading thought—The pondweed lives entirely below the water; at blossom time, however, it sends up its flower stems to the surface of the water, and there sheds its pollen, thus securing cross-pollenation.

Method—As this is primarily a lesson that relates to geography, the pondweed should be studied where it is growing. It may be studied in the spring or fall, and the pupils asked to observe the blossoming which occurs in late July. After the pupils have seen where it grows, the plants themselves may be studied in an aquarium, or by placing them in a pail or basin of water. There are confusing numbers of pondweeds but any of them will do for this lesson. The one described in the Teacher’s Story is probably P. perfoliatus.

Observations—1. Where is the pondweed found? Does it ever grow out of water? Does it ever grow in very deep water? Does it ever grow in swiftly flowing water?

2. Has the pondweed a root? Does the pondweed need to have water carried to its leaves, as it would if it were living in the air? What is one of the chief uses of the roots to the pondweed? Break off a plant, does it float? Do you think it would float off and die, if it was not anchored by its root?

3. Compare the stem of pondweed with that of any land plant standing straight. What is the chief difference? Why does the pondweed not need a stiff stem to hold it up? Cut the stem across, and see if you can observe why it floats?

4. Examine the leaves. Are all of them below the surface of the water? If some float, how do they differ in texture and form from those submerged? How are they arranged on the stem? Are they set close together? What is the difference in texture between its leaves and those of the jewelweed, dock or any other land plant? If any leaves project out of the water are they different in form and texture from those submerged? Sketch the leaf, showing its shape, its edges, and the way it joins the stem.

5. How far below the surface of the water does the pondweed usually lie? Does it ever rise up to the water’s surface? When? Have you ever noticed the pondweed in blossom? How does the blossom look on the water? Can you see the white pollen floating on the surface of the water? Look down into the water and see the way the pondweed stands in order to float its blossoms.

6. Study the blossom. Note the stem that bears it. Is the part that bears the flower enlarged and stiffer than the stem below? Do you think that this enlarged part of the stem acts like the bob on a fish-line? Examine a flower cluster with a lens. How many flowers upon it? Study one flower carefully. Describe the four stigmas at the center. Describe the anthers arranged around them. Describe the sepal which protects each anther. When the anthers open do they discharge the pollen toward or away from the stigmas?

7. What happens after the flowers are pollenated? Do they still float? What sort of seed-capsule has the pondweed? Do the seeds break away and float?

“Again the wild cow-lily floats
Her golden-freighted, tented boats,
In thy cool caves of softened gloom,
O’ershadowed by the whispering reed,
And purple plumes of pickerel weed,
And meadow-sweet in tangled bloom.

“The startled minnows dart in flocks,
Beneath thy glimmering amber rocks,
If but a zephyr stirs the brake;
The silent swallow swoops, a flash
Of light, and leaves with dainty plash,
A ring of ripples in her wake.”

—“Birch Stream”, Anna Boynton Averill.