UPPER PALEOZOIC FLORAS 157 



1. The tremendous size and great height of the types, and their 

 rank foHar development, indicating favorable conditions of environ- 

 ment and vigorous nutrition. 



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 decom 

 position 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 Crypto- 

 gams 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 cycada- 

 lean 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 equability, extending, without 



