CLIMATOLOGY OF THE LATE PALEOZOIC 243 



"2. The succulent nature of many of the forms, the large size of the vessels 

 and cells, and the relatively great proportion of soft tissue, all indicating rapidity 

 of growth in a moist, mild climate. 



"3. Spongy leaves suggestive of a moist atmosphere, and abundant and 

 large intercellular spaces, as in the lycopods, pointing to rapid moisture-loss; 

 also water-pores for disposal of excess of moisture. 



"4. Stomata placed in grooves, as in the lycopods, as if to prevent obstruction 

 by falling rain. 



"5. Absence of annual rings in the woods; hence absence of marked seasonal 

 changes. 



"6. The analogies of the present day show [that] aerial roots, so prominent 

 in many of the Carboniferous types, are characteristic of moist and tropical 

 climates; that the nutrition — i. e., the decomposition of CO2 — is most rapid 

 and the consequent growth also greatest and most rapid where the light is not too 

 strong; that the ferns and lycopods, so abundant in the Paleozoic, usually avoid 

 bright glare. The same types are able to withstand larger amounts of CO2 with 

 benefit to themselves. 



"7. The nearest living relatives of the Paleozoic vascular cryptogams reach 

 their greatest size in humid and mild or warm climates. The successors of the 

 marratiaceous and gymnospermous types are now mostly confined to tropical 

 or subtropical regions. The cycadalean stock, now characteristic of the same 

 zones, was actually present in the upper Coal Measures. 



"8. The formation of great amounts of coal indicates a rank growth, but in a 

 temperature not so warm as to promote decay beyond the limit of rainfall 

 protection. 



"9. Living nearest representatives of Paleozoic fishes now inhabit the estuaries 

 of warm countries; while the nearest relatives of the Carboniferous insects are 

 now found in mild and moist habitats. 



"10. The most forcible argument, after all, for an equable and uniform climate 

 lies in the extraordinary geographical distribution of the floras in relative unity 

 over the face of the earth. Humidity must naturally have attended such equa- 

 bility, extending, without distinct terrestrial climatic zones, possibly completely 

 into the polar regions. 



"Some of the criteria above mentioned are susceptible of different inter- 

 pretations; but taken collectively they appear to admit of but one conclusion. 

 Whether or not we admit that climatic changes may be caused by reasonable or 

 practicable changes in the amount of carbonic-acid gas in the air, it is certain that 

 in geological times the vegetation of the earth must have been more or less in- 

 fluenced by the constitution of the atmosphere from which the plant derives 

 so important a part of its real food. * * * 



"As has already been indicated, the Westphalian probably witnessed the 

 greatest extension of uniformity and equability of climate over the earth. In 

 the Stephanian the flora is hardly so homogeneous, though the world-climate 

 appears still to have been so equable as to allow free migration of the larger part 

 of the flora from a moderate latitude on one side of the equator to the opposite 

 without encountering seriously obstructive seasonal changes. In the Permian 

 the regional distinctions between the floras are much clearer; and presently 

 climatic zones, and consequently botanical provinces, are recognized. Yet, about 

 the North Atlantic the climate of the Lower Permian was still relatively uniform, 

 so that moderately free migration of the floras without the development, so far 



