394 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1918. 



The Taxales are less clearly recognizable in collections of Jurassic 

 plants, although their variety and abundance in the preceding late 

 Triassic and in the succeeding Lower Cretaceous, gives certainty to 

 the assumption of their presence through the intervening Jurassic. 

 The order Coniferales, which includes the majority of the existing 

 Coniferophytes, is well represented during the Jurassic, especially 

 by members of the family Cupressaceae, to which Brachyphyllum 

 (Eehinostrobus), Widdringtonites, Palaeocyparis, Cyparisidium, 

 and other genera, are referred. 



The family Taxodiaceae is doubtfully represented by Leptostrobus, 

 and Sequoia appears in the record before the close of the Jurassic. 

 The relatively modern family Abietinaceae is of little importance 

 until later times, and its presence during the Jurassic rests upon 

 somewhat inconclusive remains of Abietites (Pinites), Holochloris, 

 etc. Kather common Jurassic Coniferophytes of unknown botanical 

 affinities are Fieldenia and Phoenocopsis, thought to be related to the 

 Ginkoales. 



A picture of the flora at any time during the Jurassic would show 

 nothing like the lofty forests of the Paleozoic or of Tertiary and 

 modern times. The Jurassic floras, whether of swamp or upland, 

 as known, consisted primarily of ferns, cycads, and conifers. The 

 ferns were all forms of moderate size. None of the cycad-like forms, 

 so characteristic of this age of earth history, were lofty; probably 

 none were as tall as an old existing individual of Cycas, and the 

 Jurassic cycads are more comparable in appearance to what is com- 

 monly denoted by the term " scrub." Kising above the general low 

 level of this scrub were the various Coniferophytes, which may have 

 predominated in more or less pure stands at certain localities, and 

 among which the Jurassic representatives of the maidenhair tree 

 (Ginkgo) stand out prominently. 



THE LOWER CRETACEOUS FLORAS. 



Lower Cretaceous plants are known from all of the continents 

 except Antarctica, and they are particularly abundant in North 

 America and Europe. The two most extensive floras are those 

 of the Potomac group of Maryland and Virginia, and those of 

 similar age from the opposite side of the Atlantic in southern Portu- 

 gal. These afford valuable comparisons for shedding light on the 

 place of origin and the migrations of the various types. A third 

 large Lower Cretaceous flora is that of the so-called "Wealden of 

 England, Belgium and Germany. Other floras of this age are 

 found in South Africa and eastern Asia, as well as in Spitzbergen, 

 Australia. New Zealand, and Greenland. 



While the known Lower Cretaceous floras necessarily represent 

 but a small percentage of the species which clothed the earth dur- 



