Page:Popular Science Monthly Volume 16.djvu/482

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THE POPULAR SCIENCE MONTHLY.

manifest, and we soon find ourselves in the presence of a new flora, where the carboniferous types have disappeared, but where, except some rare monocotyledons, the angiosperms are still wanting. Always cryptogams and gymnosperms, the first represented by ferns and Equesitaceæ, the second by Cycadeæ and conifers. From Spitzbergen to Hindostan, from Europe to Siberia, everywhere the same vegetable forms, so that the character of the Jurassic flora is monotonous, lifeless, and relatively indigent. However, we quickly perceive two sorts of vegetation: one peculiar to low and humid plains, including beautiful ferns and Cycadeæ (Fig. 6); and the other covering the hilly regions, and composed of different genera of the same families, but chiefly of tall conifers, which in great part composed the forests of that time.

PSM V16 D482 Characteristic jurrassic plants.jpg
Fig. 6.—Characteristic Jurassic Plants; Types of Cycadeæ or Humid Localities: 1. Podozamites distans (Presl.); young plant. 2. Pterophyllum Jaegeri (Brongn.); summit of a leaf. 3. Pterozamites comptus (Schim.); interior part of a leaf.

We know not under the influence of what conditions organic evolution, and especially the appearance of dicotyledons, has taken place; but we do know that from the horizon of the cenomanne chalk commenced the neophytic period, these plants appear in a multitude of places and multiply with great rapidity. Wherever the cenomanien is found we find the remains of that age, proving the predominance of dicotyledons and the decrease of Cycadeæ and conifers. "This revolution," says Saporta, "has been as rapid in its progress as universal in its effects." It would certainly be interesting to follow the author in his enumeration of the ancestors of our common plants, and his description of the progenitors of the poplar, the beech, the ivy, the chestnut, the plane-tree and others, but it would extend this article beyond the limits of our space. Besides, we have followed vegetable evolution through its principal phases—that is to say, we have in some