OKLAHOMA ACADEMY OF SCIENCE 41 



will select practically all other available trees before taking syca- 

 more. 



The genus Platanus has had a rather remarkable life history. 

 In its time it was king of the forest. At the time when the oak, 

 the elm, and the maple were small, insignificant forms, struggling 

 .'or existence, the Platanus was one of the predominating types, with 

 nearly a score of species, many of them very abundant, bearing 

 large leaves, some of which were 18 inches in diameter. 



The story of the Platanus has been preserved in the rocks. 

 The strata of every geological age from Lower Cretaceous to the 

 present have contributed to the record of the life history of the 

 type. By studying the imprints of the leaves preserved in the 

 rocks one can read the story of the incipiency, the gradual growth 

 and development, the culmination, the decadence, and almost of 

 the death and extinction of the genus. 



Dicotyledons first became conspicuous in the Lower Cretaceous, 

 although they are known to occur in the Jurassic and even Trias- 

 sic rocks. It so happens, however, that there have been very few 

 leaf-bearing strata discovered in either the Triassic or Jurassic 

 in Europe or America, and for that reason the phytopaleontologist 

 is often at a loss for material to complete the record. The old 

 Palaeozoic types, consisting largely of gigantic ferns, club mosses, 

 horsetails, and rushes, that made up the coal plants, had culminat- 

 ed during the Pennsylvanian and Permian times, while in Triassic 

 times they took on their lowly and subservient place in the plant 

 kingdom which they have since retained. As the lower forms de- 

 clined, the higher types increased, both in number of species, in 

 abundance, and in size. During Jurassic and Triassic times there 

 was considerable development of genera and species of dicotyle- 

 dons, but unfortunately the record is nearly lost, or at least, it has 

 not yet come to light in Europe and North America. It is to be 

 hoped that in some of the practically unknown regions of Asia, 

 Africa, South America, or in the Artie regions, Triassic or Jur- 

 assic leaf-bearing strata will yet be discovered which will enable 

 the plant paleontologist to complete his record. 



At the beginning of the Comanchean, or Lower Cretaceous 

 age, there was revealed such a wealth of dicotyledons as the world 

 had never before seen. Scores of genera, and hundreds of species, 

 of well developed forms are preserved in the rocks. The Amboy 

 clays of New Jersey, the Eutaw beds of South Carolina, the 

 Tuskaloosa formation of Alabama, the Cheyenne sandstone of 

 Kanse.s, the Koonenia beds of the Northwest, have all contributed 



