We could hardly leave the Carboniferous time without at least brief mention of the ginkgo tree ([Figure 109]), or, as some call it, the maidenhair tree. From the upper strata of the Carboniferous it is common, as it is in practically all subsequent fossil accumulations down to the most recent. And yet the tree has never been found wild, although its frequency in temple gardens in China and Japan, always as a cultivated tree, suggests that its disappearance as a wild plant must have come since the priests began preserving it, which can be only a matter of a few thousand years at most. In other words, we have just missed seeing in the ginkgo what has so many times happened to these very ancient types of vegetation, namely, their final extinction. This must have occurred within historic times, and, judging by its frequent use as a temple tree in eastern Asia, that region was its last outpost after its long journey from the dim past. Thousands of other ancient plants have completely disappeared, and one cycad from New South Wales is at this moment putting up a losing fight against modern competitors, but in the ginkgo tree the actual twilight and extinction of its wild existence has missed observations by modern plant geographers by only a brief period. It is almost as though we had waited all our life to see some great event and then missed it by a few moments. Fortunately the tree is now common in cultivation, and not the least interesting feature of it is the fact that its male fertilizing cell retains its power of movement, which dates back to its early associates. Among modern flowering plants only the ginkgo and the relatives of the sago palm or cycads retain this relic of an overwhelmingly cryptogamous ancestry.
The end of the Carboniferous or coal-forming ages was marked by great changes in the earth’s surface, some of them cataclysmic in their effects. What they were in detail is described in the volume on geology and need not be repeated here. What happened to the development of the plant kingdom after this will be considered in the next section of this chapter.
4. More Recent Ancestors of Our Modern Flora
The vegetation at the ending of Carboniferous times was much affected by the great changes in the earth’s surface which happened then. The thrusting up of great mountain chains, the slow encroachment of continental glaciers, and the other phenomena characterizing that period could not but be reflected in the plant population. For one thing the giant club mosses and horsetails were much reduced in extent and finally disappeared, leaving only the immediate ancestors of our present-day forms. Cordaitales gave place to trees not unlike some of the modern yew trees. True ferns as well as the cycadlike ferns with seeds appear to have lived side by side with true cycads, which subsequently supplanted their obvious cycadlike fern ancestors. There was an obvious dwindling of ancient Carboniferous forms, some of which, however, persisted in considerable numbers. Many other plants existed then, some of which died out there, and some of which still survive in descendants, particularly among our conifers and ferns. But there happened toward the upper end of this period an event in the history of the plant kingdom so dramatic, of such far-reaching results, that its appearance might be likened to the overthrow of the Czar in Russian history or to the downfall of the Kaiser in Germany. For with it dawned a new era for the plant world, the effects of which we see all about us to-day.
Somewhere in the rock strata of this period we find the first angiosperm, or plant that matures its seed in a closed ovary, and with the origin of that habit there began such a development of plants of this type that its impetus has not yet been lost. It is impossible to tell at this distance from the origin of that first angiosperm from what it developed, nor how many ages it may have existed before the accident of its preservation as a fossil revealed its presence. It is certainly not without significance that it bore conelike fruits, such as all its associates and predecessors among flowering plants had done, but its possession of large, showy petals is the first evidence of a flower characteristic that was destined to make our present vegetation the lovely thing it is. This exceedingly interesting plant was a Magnolia ([Figure 110]), or so like our present plants of that genus as to be their obvious ancestor. Somewhere here, too, must have arisen the insect fertilization of flowers which we have seen to be such an important part of flower economy at the present time. Most of this ancient magnolia’s associates must have relied on wind pollination for seed production, as many modern plants still do, but the origin of insect fertilization appears to have come with the appearance of the first really petaliferous flower.
