Lesson CXL

The Common, or Lance-leaved, Thistle

Leading thought—The thistle is covered with sharp spines, and these serve to protect it from grazing animals. It has beautiful purple flowers, arranged in heads similar to those of the sunflower.

Method—A thistle plant brought into the schoolroom—root and all—and placed in water will serve well for this lesson. The questions should be given the pupils as to where thistles are found. Any thistle will do for the lesson.

Observations—1. Where do you find the thistles growing? Do you find more than one species growing thickly together? Do you find any of the common thistles growing in soil which has been cultivated this season?

2. Describe the stalk, is it smooth? Is it weak or strong and woody? What sort of root has it?

3. Do the leaves grow alternately or opposite? Are they smooth or downy on one or both sides? Do the spines grow around the margins, or on the leaves and veins? Are the leaf edges flat, or wavy and ruffled?

4. How does this affect the direction in which the spines point? Are the leaves entire or deeply lobed? Have they petioles, or are they attached directly to the stalk?

5. Note if any buds or small branches nestle in the axils of the lower leaves. What effect does cutting the main stalk seem to have on each side shoot?

6. Do the flower-heads of the thistle grow singly or in clusters? Do they come from the summit of the stalk, or do they branch from its sides? Which blossom-heads open first—the topmost or those lowest on the stalk? Are the flowers fragrant? What insects do you most often see visiting thistle blossoms for pollen or nectar? Study the thistle flower according to Lesson CXXXV.

7. Carefully study a thistle balloon. How is the floss attached to the seed? Is it attached to the smaller, or the larger end? Hold the thistle balloon between your eye and the light. Does the down consist of single separate hairs, or have they many fine branches? How is the down arranged when all the flowers are packed together in the thistle-head? Take a seed from among its closely packed fellows in the thistle-head, and put it in the sun or in a warm, dry place where it cannot blow away. How long does it take for the balloon to open out? What is its shape? Is there any down at the center of the balloon or is it arranged in a funnel-shaped ring? Can you find a perfectly globular thistle balloon with the seeds still attached to it? How far do you think the thistle balloons might travel?

8. If a thistle seed finds a place for planting during the autumn, how does the young plant look the next season? Describe the thistle rosette. What growth does it make the second summer? What happens to it then?

9. Why can you not cultivate out the Canada thistles as you can the other species?