142 DAVID WHITE 



Place of origin. — Though eastern America has contributed most to 

 our knowledge of this flora, it is probable that either the estuaries of 

 northwestern Europe or the Arctic regions offered the conditions 

 most favorable for its development. It extended both east and west 

 in a high degree of unity. For example, the flora which occurs in 

 the "Chapman" sandstone in Maine, and which is present in the 

 gulf region of Canada, is largely the same as that of Scotland, at 

 Burnot in Belgium, or in the Lenne shales of the Rhine Provinces. 

 The flora from Barrande's H-h, stage at Hostim in Bohemia is nearly 

 counterfeited in the upper Middle Devonian of New York. The 

 route of migration between Europe and America was presumably 

 by Arctic lands beyond the North Atlantic. Nothing that can be 

 called a land flora is yet known from the Middle Devonian of the 

 Southern Hemisphere. 



UPPER DEVONIAN 



Floral characters. — Evolution of forms and the advent of new 

 types mark the Upper Devonian flora, which bears no evidence of 

 any great climatic separation from the preceding. Pseudobornia, 

 perhaps first of the Protocalamariales, Dimeripteris, Leptophleum, 

 Barrandeina, and Barinophyton are characteristic. It is pre-emi- 

 nently the stage of Archaeopteris. The Protolepidodendreae are 

 developing along divergent lines to Cyclostigma and to the Carbonif- 

 erous Lepidodendron, while Archaeosigillaria makes its rare appear- 

 ance. 



Place of origin and migration. — I am strongly inclined to believe 

 that this flora received its greatest contribution from eastern America, 

 or, perhaps, from the Arctic regions; in either event its migration 

 was probably over boreal land; for it extends with remarkable 

 identity from Pennsylvania to southern Europe and is partially 

 present even in Australia. Archaeopteris obtusa and A. sphenophyl- 

 lifolia of Pennsylvania and New York are A. archetypus and A. 

 fissilis of Ellsmere Land, Spitzbergen, and the Don; while Barino- 

 phyton, a unique type from New York, Maine, and Canada, extends 

 to the British Isles, Belgium, Queensland, and Victoria, where also 

 is found Leptophloeum rhombicum, another x^merican plant. 



The Devonian woods present no annual rings to bear evidence of 

 seasonal changes in temperature or intervals of prolonged drought. 



