CLIMATOLOGY OF THE LATE PALEOZOIC 237 



the leaves in many species; (d) protection of the stomata in dorsal canals, for 

 example, Sigillaria, as though to prevent flooding, but possibly 'pseudoxero- 

 phytic ' in origin ; (e) great differentiation and vast predominance of pteridophytic 

 forms, including many widely varied heterosporous types to whose prolific 

 fertilization a very wet habitat is most essential; (/) smooth, hard, persistent 

 outer bark; (g) adaptation of nearly all types to fertilization in a rainy habitat, 

 such as protection of pollination and probable flotation of immature seeds; (A) 

 flotation devices possibly peculiar to swamp types; (') prevalence of great 

 swamps on coastal or inland base-level peneplains, and of great amounts of un- 

 decayed vegetal matter remaining either in stratified masses as coal or in the 

 carbonaceous shales and other terrigenous deposits; (j) formation of much 

 xyloid coal, requiring abundant humidity in a climate of mild temperature. 



' ' That the climate was warm is further shown by : (a) the rank, luxuriant growth 

 and large size of the plants, especially of cryptogamous types; (b) the rapid, succu- 

 lent growth, with large cells; (c) the dense, large undergrowth; (d) the many 

 long climbing or clambering filicoid types, including a considerable number of 

 membranaceous delicate forms; (e) the present tropical habitats of living repre- 

 sentatives (e. g., Marratiaceae and Gleicheniaceae) nearest related to Carboniferous 

 types, whereas the habitats of the Coal Measures cycad stock are tropical or 

 subtropical; (/) the attainment of gigantic size by the equisetales (so common 

 and highly differentiated in the Coal Measures, and to-day always growing in 

 moist ground), only under warm or mild equable conditions. 



"Additional evidence of high importance is found in the absence of growth 

 rings; that is, continuity of growth, indicating absence of winter frosts or of 

 long or severely dry seasons unfavorable for the vegetative process. Equability 

 also may be predicated on the seemingly almost worldwide range of mildness of 

 climate. 



" Proof of relative uniformity in climate is based mainly on the extraordinary 

 radial distribution of identical species in all lands, even in high latitudes. Prac- 

 tically entire floras spread over the earth, crossing the equator, seemingly without, 

 so far as noted, experiencing seriously obstructional climatic differences or seasonal 

 changes. Minor differences between the floras of certain regions, for example, 

 the coastal districts and the inland fresh-water basins, and the absence of certain 

 genera or species from one continent or another, have been noted by Gothan 1 

 and White,* but as between continents, the comparatively uniform distribution 

 of the floras, although less than is sometimes stated, is a remarkable feature of 

 the period, being most nearly comparable to that of the mid-Jurassic. 



"Many identical Westphalian species, including a number characterized by 

 short duration, range across the coal fields of North America and Europe to 

 Persia and China, and a few occur in the Arctic Zone, in South Africa, and in 

 Argentina. It is probable that during "Lower" and "Middle" Coal Measures 

 (Pottsville) time, at least, no zone of torrid heat, as contrasted with polar tem- 

 peratures, existed in the equatorial regions. On the other hand, it is probable 

 that over most of the earth, at least outside of the polar circles, the temperatures 



1 Gothan, \V., \Veiteres fiber floristische Differenzen (Lokalfarbungen) in der europaischen 



Carbonflora, Zeitschr. Deutsch. geol. Gesell., vol. 61, No. 7, 1909, pp. 313-325; 



Pflanzen-geographisches aus der paleozoischen Flora, Zeitschr. Deutsch. geol. Gesell., 



vol. 59, 1907, p. 150. 

 * White, David, The Upper Paleozoic Floras, Their Succession and Range, Jour. Geol., 



vol. 17, 1909, p. 328. 



