Anna B. Comstock

The Thistle

Teacher's Story

N looking at the thistle from its own standpoint, we must acknowledge it to be a beautiful and wonderful plant. It is like a knight of old encased in armor and with lance set, ready for the fray. The most impressive species is the great pasture, or bull, thistle (C. pumilis),  which has a blossom-head three inches across. This is not so common as the lance-leaved thistle, which ornaments roadsides and fence corners, where it may remain undisturbed for the necessary second year of growth before it can mature its seeds. The most pernicious species, from the farmer's standpoint, is the Canada thistle. Its roots are perennial, and they invade garden, grain field and meadow. They creep for yards in all directions, just deep enough to be sure of moisture, and send up new plants here and there, especially if the main stalk is cut off. Roots severed by the plow, send up shoots from both of the broken parts. Not so with the common thistle, which has a single main root, with many fibrous and clustered branches but with no side shoots.

Lance-leaved thistle.

The stalk of the lance-leaved thistle is strong and woody, and is closely hugged by pricky leaf stems, except for a few inches above the root. The leaves are placed alternately on the stalk; they are deep green, covered above with rough and bristling hairs, and when young are covered on the under side with soft, gray wool which falls away later. The spines grow on the edges of the leaves, which are deeply lobed and are also somewhat wavy and ruffled, thus causing the savage spears to meet the enemy in any direction. The ribs and veins are without spines. Small buds or branches may be found at the axils of the leaves; and if a plant is beheaded, those axiliary buds nearest the top of the stem will grow vigorously.

The thistle flowers are purple in color and very fragrant; they grow in single heads at the summit of the stalk, and from the axils of the upper leaves. The topmost heads open first. Of the individual flowers in the head, those of the outer rows first mature and protrude their pistils; the pollen grains are white. In each flower, the corolla is tube-shaped and purple, parting into five fringelike lobes at the top, and fading to white at its nectar-filled base.

A floret from a thistle flower-head.

The stamens have dark purple anthers, united in a tube in which their pollen is discharged. The pistil, ripening later, shoves out the pollen with its stigma, which at first is blunt at the end, its two-parted lips so tightly held together that not a grain of its own flower's pollen can be taken. But when thrust far out beyond the anther-tube, the two-parted stigma opens to receive the pollen which is brought by the many winged visitors; for of all flowers, the thistles with their abundant nectar are the favorites of insects. Butterflies of many species, moths, beetles and bees—especially the bumblebees—are the happy guests of the thistle blooms.

The thistles believe in large families; a single head of the lance-leaved thistle has been known to have 116 seeds. The seeds are oblong, pointed, little akenes, with hard shells. Very beautiful and wonderful is the pappus of the thistle; it is really the calyx of the flower, its tube being a narrow collar, and the lobes are split up into the silken floss. At the larger end of the seed is a circular depression with a tiny hub at its center; into this ring, and around the knob, is fitted the collar which attaches the down to the seed. Hold the balloon between the eye and the light, and it is easy to see that the down is made of many-branched plumes which interlace and make it more buoyant. When first taken from its crowded position on the flower-head, the pappus surrounds the corolla in a straight, close tube; but if placed for just a few moments in the sun, the threads spread, the filmy branchlets open out, and a fairy parachute is formed, with the seed hanging beneath; if no breath of air touches it while spreading, it will sometimes form a perfect funnel; when blown upon, some of the silken threads lose their places on the rim and rise to the center. When driven before the breeze, this balloon will float for a long distance. When it falls, it lets go of the seed as the wind moves it along the rough surface of the ground, and when it is thus unburdened the down fluffs out in every direction, making a perfect globe.

For the first season after the seed has rooted, the thistle develops only rosettes, meanwhile putting down roots and becoming permanently established. The next season, the flowers and seeds are developed, and then the plant dies. Would that this fact were true of the Canada thistle; but that, unfortunately, is perennial, and its persistent roots can only be starved out by keeping the stalks cut to the ground for the entire season. This thistle trusts to its extensively creeping rootstocks more than to its seeds for retaining its foothold and for spreading. While it develops many seed balloons, a large number of its seeds are infertile and will not grow.

The Canada thistle. Drawing by W. C. Baker.

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.

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?