5. Present-Day Plants and Where They Come From
There are living to-day somewhere about 150,000 species of flowering plants; half a hundred conifers or gymnosperms; about 3,500 ferns; 500 club mosses; over 70,000 bacteria, fungi, and lichens, and probably over 20,000 species of algæ. The estimates of the last three divisions are more or less uncertain, as many species are still being discovered.
From what has just been read regarding the plants of earlier periods it is at once clear how completely the flowering plants have conquered all their ancient forbears, and what a pitifully small remnant of once proud and ancient forests are now represented by our club mosses and horsetails. That process of crowding, of the dominance of one kind to the exclusion or even extinction of others is still going on, and, as we shall see in the last chapter, often on a great scale.
If the period just after plants were first known on the earth may be called the Reign of Algæ, and subsequent periods were typified by still other kinds of plants, then our present period is par excellence the reign of flowering plants. In numbers of individuals they are still far outclassed by such cryptogams as the fungi, bacteria, algæ, etc., but their dominating influence in the plant world is unquestioned.
While all our present vegetation must have been derived from preexisting types, all of it is not necessarily directly descended from species which from their fossil records we know to have existed in geological periods older than our own. While the fossil record of the times immediately preceding the last ice age is a much more complete one than for many other periods, it fails to account directly for the great bulk of our varied flora of to-day. While ferns in great variety, gymnosperms, and hundreds of flowering plants are known quite definitely, they total only a minute fraction of these groups to-day. Even granting the always imperfect nature of the fossil record, and we have seen what an accident the formation of a plant fossil may be, and it is common knowledge how few comparatively have ever been recovered—even granting all this, there still remains a large part of our present flora of which the origin probably dates from comparatively recent times. So overwhelmingly true is this that of the Compositæ, or daisy, family, now numbering over 11,000 species, scarcely a handful of fossil species have been found. And in all collections of fossils the woody plants far outnumber the herbs, perhaps because of the greater probability of their being thus preserved rather than to any actual scarcity of herbs in the upper strata. And yet herbs to-day outnumber woody species over two to one. While it is true, then, that our present flora must have been derived from preexisting races, it is also true that much of it is apparently derived from plants that do not date very far back into the past. A few main types of flowering plants unquestionably are to be linked with fossil genera, but these types have now branched out into a wealth of detail that may not have existed and is certainly not recorded in the fossil record.
Some of these types stand out with remarkable clearness, notably magnolia, willows, poplars, walnuts, birches, oaks, figs, sassafras and its relatives, the rosales, the pea family, the spurges, maples, grapes, linden, myrtle, ginseng, and some others. All these, and in not very different aspect from their modern representatives, have been found in the fossils of the different and usually more recent strata before the last Ice Age. But the total fossil record of even these well-known genera is only a fraction of their modern development, and we are constantly confronted with the apparent dilemma of accounting for a present wealth of forms based upon an obvious poverty of ancestry. While the whole race of flowering plants is certainly a new one, as such things are reckoned fossilwise, there has been a fecundity in the origin of new species among these lusty upstarts that is simply amazing. How that, in part at least, has been accomplished will be considered in the final section of this chapter. Not only among these present-day plants, but all through the story of the development of the plant kingdom, we have been reading and writing of the changes of form and structure, some of which have been of far-reaching consequences. It is clear enough that if new types of vegetation and different races of plants have come into being and so modified the complexion of the plant kingdom, those changes must have first arisen in individuals which had within them some capacity for change, and furthermore the ability to use the change to their advantage. While, as we have seen, the losses have been tremendous, no one, with even this brief history of their development in mind, can doubt that there has been progress toward our present perfection of plant life.