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But with the fresh upheaval and climatic disturbance at the end of the Jurassic, and during the Cretaceous, they spread northward, and replaced the dying reptiles, as the Angiosperms replaced the dying cycads. When they met the spread of the Angiosperm vegetation they would receive another great stimulus to development. They appear in Europe and North America in the earliest Cretaceous.
This remarkable double fertilization as it has been called, although only recently discovered, has been proved to take place in widely-separated families, and both in Monocotyledons and Dicotyledons, and there is every probability that, perhaps with variations, it is the normal process in Angiosperms.
But the evolution of the Angiosperms is a recent and immature study, and we will be content with a few reflections on the struggle of the various types of trees in the changing conditions of the Tertiary, the development of the grasses, and the evolution of the flower. In other words, we will be content to ask how the modern landscape obtained its general vegetal features.
The long and interesting story of the mammals must be told in a separate chapter, and a further chapter must be devoted to the appearance of the human species. We saw that the Angiosperms, or flowering plants, appeared at the beginning of the Cretaceous period, and were richly developed before the Tertiary Era opened. We saw also that their precise origin is unknown.
A similar argument is used in regard to “ontogeny recapitulating phylogeny.” Palæontology does not disclose in the plant-world any “synthetic types,” which might have been the common primitive stock from which many now divergent branches have sprung, nor does it disclose any “transition links” really intermediate, for instance, between cryptogams and gymnosperms, or between gymnosperms and angiosperms.
The orders are carefully characterized, and those of Angiosperms are grouped in fourteen classes under the two main divisions Monocotyledons and Dicotyledons.
Most probably the development of the characteristic flowers of the Angiosperms is connected with an increasing relation to insects, but what we want to understand especially is the deciduous character of their leaves. Many of the Angiosperms are evergreen, so that it cannot be said that the one change entailed the other.
Angiosperms are again divided into the monocotyledons, as the palms, and dicotyledons, which include most European trees. Thus: Adolphe Brongniart termed the coal era the "Age of Acrogens," because, as we shall see, of the great predominance in those times of vascular cryptogamic plants, known in Dr Lindley's nomenclature as "Acrogens." Spenophyllum cuneifolium.
The Angiosperms do not spread much westward; they appear next in Greenland, and, before the middle of the Cretaceous, in Portugal. They have travelled over the North Atlantic continent, or what remains of it. The process seems very rapid as we write it, but it must be remembered that the first half of the Cretaceous period means a million or a million and a half years.
The stem shows, at b, a little below the spike, remains of a lateral appendage, which is supposed to indicate the beginning of the spathe. The fossil has been referred to the Aroidiae, and there is every probability that it is a true member of this order. There can at least be no doubt as to the high grade of its organisation, and that it belongs to the monocotyledonous angiosperms. Mr.