130 L. F. Ward — Evidence of the Fossil Plants, etc. 



others, with the sole exception already mentioned, instead of 

 those plants coming in gradually, as they would be expected to 

 do if the formation represented an age at which their develop- 

 ment was inchoate, and instead of presenting rudimentary, 

 transition, and archaic types of that subclass, as such early de- 

 posits would naturally do, we find them to be the prevailing, 

 sometimes, as in the Dakota Group, almost the only form of 

 plant life, and we also find them fully developed, and even 

 w,hen most unlike our modern vegetation, still exhibiting all 

 the characters of highly organized plants of their rank. In 

 the Potomac formation, on the contrary, we find the Dicotyle- 

 *dons behaving precisely as they ought to behave in a form- 

 ation that represents an age close down to that at which this 

 form of life first made its appearance in the geologic history 

 of the globe. We find them to constitute the great rarities of 

 the flora, absent from many of the most productive beds, scarce 

 at all places in comparison with the lower types of vegetation, 

 strange and peculiar in character, so vague and ill- defined as 

 in some cases to cause doubts as to whether they really belong 

 to this group of plants, possessing features that recall the ferns, 

 Cycads, Conifers, and even the Monocotyledons, and containing 

 comprehensive types prophetic of many of the now fully de- 

 veloped families of Dicotyledons. They therefore form just 

 such a homogeneous ana undifferentiated group of plants, 

 combining in a scarcely distinguishable way all the elements of 

 the later dicotyledonous flora, as we should expect to find 

 existing during the early history of this type of vegetation. 

 They are therefore not to be' regarded as anomalous but as 

 normal, and the anomaly, if any there be, exists in Cenoman- 

 ian floras, where this type occurs in such a predominant and 

 highly developed form. 



In view of these facts I cannot accept the conclusion that 

 the dicotyledonous element of the Potomac flora argues a more 

 recent age than that denoted by the other types. On the con- 

 trary, the immense difference between this and the Cenomanian 

 floras clearly indicates that a vast period must have been 

 required to produce so great a development. 



On numerous occasions, dating as far back as 1878,* I have 

 expressed the opinion that the Dicotyledons could not have 

 had their origin later than the middle Jura, and it will not sur- 



* American Naturalist, vol. xii, June, 1878, p. 378; November, 1878, p. 734. 

 In a lecture delivered February 24, 1883, at the National Museum on Plant Life 

 of the Globe, past and present (see Science, vol. i, May 4, 1883. p. 358). Ameri- 

 can Journal of Science, third series, vol. xxvii, April, 1884, p. 302. Proc. A. A. 

 A. S., vol xxxiii. Philadelphia Meeting, September, 1884, p. 497. Botanical 

 Gazette, vol. ix, Indianapolis, October and November, 1884, p. 174. Fifth An- 

 nual Report U. S. Geological Survey, 1883-84, Washington, 1885, diagram, pi. 

 lviii, facing p. 452. 



