THE STORY TOLD BY FOSSIL PLANTS
Each successive group of plants that appeared upon the scene illustrates a second great principle, which is called “adaptive radiation”—that is, from time to time, by progressive modifications, certain groups became dominant, such as the club mosses, horsetails, and seed ferns of the Carboniferous
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Fig. 1.—Diagram showing the successive numerical dominance of progressively more complex plants through the geologic eras and the progressive increase in the complexity of the more familiar floras.
The space assigned to the several eras (Archeozoic, Proterozoic, etc.) corresponds roughly with the length of time included in them. The Archeozoic is the earliest era, the Cenozoic the latest. The heavier lines show the increase or decrease in the number of the different kinds of plants through geologic time. The flowering plants are now (in late Cenozoic time) by far the most numerous, and their rise to dominance has been rapid; yet representatives of the older forms still persist, though they are less abundant than the flowering plants.
The space assigned to the several eras (Archeozoic, Proterozoic, etc.) corresponds roughly with the length of time included in them. The Archeozoic is the earliest era, the Cenozoic the latest. The heavier lines show the increase or decrease in the number of the different kinds of plants through geologic time. The flowering plants are now (in late Cenozoic time) by far the most numerous, and their rise to dominance has been rapid; yet representatives of the older forms still persist, though they are less abundant than the flowering plants.
period, the cycads of the Mesozoic era, or the flowering plants of the Cenozoic era. The members of these groups became adapted to a great variety of environment and tended to occupy all the available places on the land, and some of them, such as the water ferns or the higher
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