Not all the geological changes which have remodeled the earth’s surface have been mentioned in this brief history of those plants that preceded our own, nor have anything like all the plants occurring in the different strata been even hinted at. But the thing which has been stressed and for us to fix in our minds is that all our present vegetation literally has its roots deep down in the earth. Some, as _Lycopodium Selago_, go back no one knows how many millions of years; others, like the flowering herbs, are much more recent. We come to understand how recent we are and what a comparatively brief flash in the pan all our modern development both of plants and in man has been since the last glacial period only by looking for a moment at what has happened in the past. In the account of the Carboniferous plants we found that there remained after that period only about 19 per cent of the earth’s age in which all the changes since then could have come about. If, as may well be possible, this period has been about 19,000,000 years, then the mere 40,000 years since the last Ice Age seems a brief period indeed. As some one has written, to contrast all man’s historic period, back to the days of the most ancient Chinese manuscript, with that long journey from the dim past which the plant world has slowly accomplished, is to realize that we are “as the flashing of a meteor through the sea of night.” Fossil plants then, and this delving into the dead past of the plant world, reveals to us as nothing else can how much the modern plant kingdom is literally built upon a mighty race of ancestors. Some perished as did the _Cordaitales_, but left descendants who themselves gave rise to other groups that survive to-day. To look over a list of the fossil plant genera of the different strata is to visualize a drama the like of which no one living will ever see replayed, the results of which are recorded all over the world with its changing panorama of vegetation. 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.