Living and extinct horsetails.—None of the British horsetails is of great height, although one species may attain to six feet. Some of the tropical members of the family, however, are very much larger than this, reaching even forty feet. In spite of the last-named fact it is quite plain that the horsetails have had their day, and are dying out. If we wish to form an idea of what they were at the height of their prosperity, we must carry our minds back to the long distant age when our coal was being formed; when so much of this country as then existed was low-lying swamp, covered with exuberant vegetation. Then the horsetails and their relatives were stately forest trees, and at the head of the vegetable kingdom. Some of them towered to a height of over ninety feet. Nor did mere height constitute the only difference between them and their degenerate descendants. Many of these old-world giants had already found out the device, since invented afresh by more modern plants, of thickening their stems and roots with secondary wood, and of giving rise to bark like that of our present-day forest trees. The wood of these Calamites (Fig. 155), as they are called by [Pg 197] geologists, had already reached much the same stage of development as is found to-day in such a tree as the yew. The cones often show great variation from the comparatively simple form found in the modern horsetail, but they are essentially of the same type. Flowering and flowerless plants.—Botanists divide plants into two great groups—flowering plants, which reproduce themselves by means of pollen grains and ovules; and flowerless plants, which still retain the primitive marriage customs of their ancestors. The flower is a comparatively recent invention in the history of plant life, and its success is shown by the dominant position in the plant world which the flowering plants now occupy. Many of the flowerless plants—like the horsetails—have fallen behind their competitors. The ferns, in spite of their conservatism, still hold their own, and seem in no danger of extinction. Many other flowerless plants maintain their position by sheer force of numbers. Yet others have become completely extinct, and can now be known only by their fossil remains. But these latter are sometimes so distinct that stems, roots, and spore-boxes can be seen with all their sharpness of outline unimpaired; the delicate tracery of frond and leaf is visible, as clear and fresh as if made yesterday. And such rocky herbaria tell us in unmistakable terms that our forest trees and other flowering plants are after all mere parvenus and upstarts. EXERCISES ON CHAPTER X. 1. Explain the formation of the green scales which are frequently seen on the surface soil of a fernery. Whence do they arise? What happens to them if they are allowed to grow? (King’s Scholarship, 1902) 2. Point out the differences between the fronds of a fern and the leaves of most flowering plants. (1901) [Pg 198]