| Gilia | Gilia capitata |
| Three-colored chrysanthemum | Chrysanthemum carinatum |
| Mourning bride | Scabiosa atropurpurea |
| China asters | Callistephus chinensis |
| Everlasting | Helichrysum bracteatum |
| Didiscus | Trachymene cœrulea |
CHAPTER VII
HISTORY OF THE PLANT KINGDOM
1. Dawn of Plant Life On Earth
“And the Earth was without form and void”
THE quotation from the second sentence of the first chapter of Genesis tells us more in eight words than could very well be said in as many chapters. Not only have we biblical authority for this early absence of life on the earth, but all the accumulated knowledge of the ages points in the same direction. We have already seen that plants, because they can take inorganic substances from the earth and air and transform them into organic food, must in all probability have come on the earth before animals which, directly or indirectly, all rely upon plants for their food. Even those animals that eat only flesh devour other animals which depend upon plants for food. It may safely be repeated, then, that upon plants all animal life depends, and that, in the dim beginnings of things on the earth, it must have been some form of plants that were the first living things. Extremely simple unicellular animals, however, are known to date from early times.
In the volume devoted to that subject in this series, you will find that at the very earliest stages of what we know as our globe there was a segregation of land and water somewhat different from our great oceans and continents to-day in extent and area, but differing mostly in this—that much of the water was fresh and very nearly boiling hot. We have still the remnants of those great reservoirs of hot water, as our hot springs and shooting geysers only too well prove. And if all plants were as quickly killed by hot or boiling water as the common garden geranium, we should not expect any plant life to have developed upon the earth until all those great bodies of water had cooled. To have waited for that would have been to delay the appearance of plants for no one knows how many millions of years, and there is some fairly good evidence that long before normal conditions of heat and cold were established there already flourished certain kinds of plants. What those plants were is something of a speculation, and indeed exactly what they were no one knows. But in our present hot springs grow certain plants, microscopic in size, but quite obviously related to the algæ or to certain bacterialike organisms. They live with apparent comfort and reproduce themselves freely in water so hot that no other form of life will maintain itself. While there is no proof that these present plant inhabitants of hot springs, common in the West, are descended from infinitely ancient progenitors, it is a fair assumption that some organism capable of growing in warm or hot water was the first living thing to appear in a world otherwise “without form and void.”
This great question of how plants came on the earth, and particularly how from these apparently simplest organisms our whole wonderful vegetation has arisen, has always been one of the most interesting things in the history of the world. There are many different ways of studying this, and in the very earliest stages of plant development we are forced to reason, not so much by actual records or buried skeletons of the plants that probably existed then, for only a very few have ever been found, but by our knowledge of the physical and chemical requirements of unicellular plants, and those slightly more developed, and of their individual life histories. It is, for instance, certain that the first plants must have been aquatic, as no real land plants are known for hundreds of thousands of years after the earth was quite capable of maintaining plant life. The absolute necessity of water to complete fertilization in nearly all cryptogams also makes it fairly certain that water plants, and these of the simplest nonflowering type, were the first living things to be found on the earth. And it is more than a fair inference that these were inhabitants of warm or hot water. Subsequently, as the water cooled, they may well have been not unlike the green scum found on ponds to-day.
Of course, the actual origin of life itself is still as much of a riddle as it was when the ancient philosophers began to speculate about it years before the Christian era. Protoplasm, the unit or basis of all life, while its composition and growth requirements are fairly well known, has never been made in any laboratory. Nor have scientists ever been able to decide what the combination of physical and chemical forces must have been to originate it. But that from a perfectly sterile, probably steaming hot globe, there did finally develop some form of life, and that this must have been aquatic plant rather than animal life, seems not only certain, but the only hypothesis upon which all subsequent development of life must have been based. It is not necessary to ascribe the origin of life to providential inspiration nor to the meddling of strange and outlandish deities, as all savage tribes did and some more civilized peoples still do. There can, however, be no escaping the fact that life is more than the combination of physical and chemical conditions which sustain it, and that its origin has never, and may never be “explained” by merely describing the conditions which unquestionably favored its appearance. In other words, the origin of plant life throws us back upon things believed but incapable of proof, and is none the less wonderful because we cannot yet understand the probable progression of forces and materials to which it owes its origin.
Assuming, then, and we must all start with this proposition, that aquatic plants certainly, and warm or hot water plants probably, were the first living things upon the earth, what are the next steps in the history of the plant kingdom? The answer to that question involves a few simple facts in geology and, particularly, in the making of fossils, which must be understood before we can see those steps or their significance. The geological changes which have resulted in the present condition of the earth’s surface are described in the volume devoted to that subject, and will not be repeated here. But some mention must be made of the formation of fossil plants, particularly as it is upon the evidence of these that the story of the development of plant life is literally written in the rocks.