2. The Development of Land Plants
After the reign of algæ and other cryptogamous water plants, our knowledge of which is so unsatisfactory because of the incompleteness of the fossil record, there appeared the first evidences of plants that were able to live with “one foot on the land and the other in the water,” so to speak. How many transitional stages there may have been, and what relation any of these may bear to existing plants, is not known, or is, at any rate, so little understood that it is a disputed point. But somewhere about this period there did appear plants capable of living at least part of their life on the land, and possessing in their vascular system a structure of enormous advantage over their predecessors. It is pure speculation as to what this first land plant was derived from, or from what particular group of water-inhabiting plants it took some of its characteristics. Its appearance, in any case, was a dramatic event of the first importance. Not the least interesting feature of it is that the very plants of which we have indisputable evidences of being the first land plants have come down through the ages to the present day. For it is practically impossible to separate our modern representative from its ancient ancestor, despite all the tremendous changes that have been going on both in the history of the earth’s crust and in the vicissitudes of the vegetation in meeting those changes.
There is the best of evidence that these first land plants were of the club moss family, which are relatives of the ferns. One of them, representing our present Lycopodium Selago ([Figure 107]) so closely as to be practically indistinguishable, is a common type, as revealed to us in the fossil record. The present plant inhabits rich, moist, and mostly evergreen woods in the northern part of the globe, and is common in the Adirondack and White Mountains.
A club moss which has come down through the ages almost unchanged from the days when coal was being formed. Grows to-day in the north temperate zone, particularly in mountains.
Nor was the earth peopled wholly by this ancestor of Lycopodium Selago, for we find at this time, or just after it, a great development of plants of this type. Some of these were giant, treelike club-mosses that have been so well preserved as fossils that even their internal structure and spore-bearing characters are well known. Many other strange relatives of our modern club mosses flourished in those days, some of which have wholly disappeared, as have all the treelike forms. These highly organized club mosses, quite unlike any modern representative of the family, appear to have been crowded off the earth by other and subsequent types of vegetation, while Lycopodium Selago, and about thirty related species, have persisted to the present day; not precisely in all cases as they were in this dawn of a land flora, but in many cases with modern structure and reproductive processes so close to the ancestral types as to be nearly identical.
Perhaps nothing gives one a better impression of the tremendous time that must have elapsed before the appearance of these ancient club mosses than the very slight modifications from their ancient condition which their structure at the present time exhibits. While nothing is certainly known of their origin, when they first appeared they were plants with a well-developed vascular system, having stems and leaves quite unlike any of their predecessors’, and a reproductive process almost precisely like their modern descendants. In other words, if they have changed so slightly in all the millions of years since our rock-written records of them first occur, what an infinitely greater period must have elapsed down the dim vista of the ages before their appearance. Of this period, with the exception of fossil algæ, we know practically nothing, and, worst of all, the actual transition from a wholly water-inhabiting flora to these certainly land-inhabiting club mosses may never be known. For, added to the difficulty of water plants being preserved as fossils, already mentioned, is the fact that as they are the oldest, they are found in the deepest strata and, consequently, the hardest to find; and due to changes in the earth’s crust, these ancient fossil-bearing strata have often been much disturbed.
The conclusion appears to be indicated that the origin of a land flora came about with the appearance of these ancient club mosses, which are not mosses in our present-day interpretation of those plants, and that at about the same period many other plants also were found, the whole vegetation resembling nothing that exists at the present time, but many of the different kinds of this ancient flora showed unmistakable evidence of being the progenitors of many plants that exist to-day. What these were, and particularly what they accomplished, both in the history of the plant kingdom and in making the world habitable for man who did not come for millions of years after they were preparing the way, will be considered in