THK cornsK OF BIOLOGIC KVOLTTION. :>o 



prevailed in early times over those provided with two sets of 

 floral envelopes, which is far from being the case at present. 

 Our law, too, is here again exemplified in the great perfection 

 attained in those early times by such apetalous trees as the 

 poplar, the plane-tree, the fig-tree, the laurel and the sassafras. 



Polypetaly. The next step was the development of a second 

 floral envelope, which, however, had its beginnings in small, 

 strap-shaped, or even bristle-shaped petals. In our current 

 botanies as prepared by Gray, De Candolle, and Bentham and 

 Hooker, the plants having separate petals, or polypetalous 

 plants, such as the rose, buttercup, mallow, etc., are placed 

 before those having the corolla all in one piece, like the morn 

 ing-glory, honeysuckle, etc. This position is given them to in 

 dicate that the authors of these books regarded them as of 

 higher rank. But the geological history of plants teaches that 

 such, at least, was not the order of nature in their develop 

 ment. It shows that polypetalous plants were very early 

 developed. We find them at the earliest epoch at which 

 dicotyledons begin to appear in any great abundance. It is 

 true that we rarely find the flowers, and cannot say with cer 

 tainty that they were the same as they are to-day. It is quite 

 possible that trees of Cretaceous time whose leaves resemble 

 those of modern polypetalous genera may have then had 

 wholly apetalous flowers, but this is as yet mere speculation. 



In this group we have another fine illustration of the law 

 which I have stated, according to which the highest attainable 

 development of any given type of structure is early and rapidly 

 acquired. We are in the habit of regarding our magnolias, 

 our tulip-trees, and the Australian eucalypts, as among the 

 finest specimens of polypetalous plants, and yet the genera 

 Magnolia, Liriodendron, and Eucalyptus appear and are rather 

 prominent in the Middle Cretaceous floras of Europe, Green- 



