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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 

 Equesitacese, the second by Cycadeae 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 Cycadese (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. 



Fig. 6.— Chakacteristic Jurassic Plants ; Types of Ctcade^e op Hcmid Localities : 1. Podo- 

 zamites dUtans (Presl.) ; yonng plant. 2. Pterophyllum JUegeri (Brongn.) ; summit of a leaf. 

 3. Pterozamites comptus (Schim.) ; interior part of a leaf. 



We know not under the influence of what conditions organic evo- 

 lution, and especially the appearance of dicotyledons, has taken place ; 

 but we do know that from the horizon of the cenomanne chalk com- 

 menced 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 Cycadese and conifers. "This 

 revolution," says Saporta, " has been as rapid in its progress as univer- 

 sal 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 



