FIFTY YEARS OF PALEOBOTANY, 1906-I956 595 



by including fossil diatoms, charophytes, and other groups of lower plants. 



Many paleobotanical studies are more floristic, systematic, and ecological 

 in character. Outstanding among them are Dorf's study of Devonian floras 

 of Wyoming, Read's preliminary description of the New Albany Shale flora 

 (basal Mississippian) of Kentucky, White's Flora of the Hermit Shale, Ari- 

 zona, Daugherty's monograph on the Petrified Forest in Arizona, Berry's 

 numerous studies of late Mesozoic and Tertiary floras of the southeastern 

 United States, Central and South America, the corresponding studies of 

 Western American fossil floras by Chaney and his students, MacGinitie's 

 Flora of the Florissant Beds, Colorado, Hollick's Tertiary floras of Alaska, 

 and Wieland's well-known accounts of the Cerro Cuadrado Petrified Forest in 

 Patagonia and the Liassic flora of the Mixteca Alta in Mexico. Significant con- 

 tributions of this kind have come from other parts of the world, among them 

 H0eg's study of the Downtonian and Devonian flora of Spitzbergen, Halle's 

 studies of the Paleozoic floras of eastern Asia, Corsin's monographs of French 

 Carboniferous plants, Harris' exemplary studies of the Rhaetic floras of 

 eastern Greenland and of the Jurassic flora of the Yorkshire coast of England, 

 Reid and Chandler's flora of the London Clay, and many others. The evolu- 

 tion and distribution of fossil floras are recorded in Seward's Plant Life through 

 the Ages (1931), one of the most readable scientific books of our times, and 

 more compactly so in Krausel's Versunkene Floren (1950) as well as in 

 Edwards' "The Geographical Distribution of Past Floras" (1955). 



Work of this kind is obviously time-consuming and difficult to evaluate. A 

 Danish botanist, H. M. Hansen, has just published some startling figures. In 

 order to assess the value of Raunkiaer's life forms as age indicators, Hansen 

 surveyed the entire paleobotanical literature (5,000 papers) published since 

 Schimper's Treatise (1869-1874). He counted 21,000 described species be- 

 longing to 3,300 genera of higher plants ranging from Late Cretaceous to 

 the beginning of the Pleistocene. As the number of species described from 

 older strata is likely to be smaller, the grand total of known fossil plants may 

 exceed 30,000 and may even be closer to 40,000. Figures of this kind are, 

 however, tentative at best. For instance, the number of fossil cycadophytes 

 has been estimated in the tens of thousands but has never been shown to be 

 that high. Conservative estimates are certainly more probable, as no group 

 of vascular plants has ever been as successful in conquering available land 

 areas as have the angiosperms. Also, the number of fossil angiosperms de- 

 scribed and likely to be described is bound to be smaller than that of living 

 angiosperms. 



Palynology is a fairly recent, collective designation for a very active seg- 

 ment of paleobotanical research, dealing with fossil spores (sporomorphs) and 

 pollen. These organs are often found in adequate numbers and well-preserved 

 condition. Detailed studies based on these microfossils have yielded some 

 remarkable results. The synopsis of fossil spores published by Schopf, Wilson, 



