226 



CLIMATE OF CARBONIFEROUS PERIOD. 



[Ch. XI. 



more 



of those countries than with the heat of the same. Few 

 palms can live in our temperate latitudes without pro- 

 tection from the cold; but when placed in hot-houses 

 they grow luxuriantly, even under a cloudy sky, and where 



much light is intercepted by the 

 At St. Petersburg, in lat. 60° K, r 



glass 



and frame 



been successfully cultivated in hothouses, although there 

 they must exchange the perpetual equinox of their native 

 regions for days and nights which are alternately protracted 

 to nineteen hours and shortened to five. How 



much 



mi 



live, provided a due quantity of heat and moisture were sup- 

 plied , has not yet been determined ; but St. Petersburg is 

 probably not the utmost limit, and we should expect that in 

 lat. 65° at least, where they would never remain twenty-four 

 hours without enjoying the sun's light, they might still exist. 

 M. Adolphe Brongniart has observed that the great nu- 

 merical preponderance of ferns over other forms of vegeta- 

 tion in the Carboniferous era gives us ground to conclude that 

 the climate was warm and moist. It must be confessed that 

 this reasoning loses some of its force when we consider that 

 the ancient flora is almost entirely destitute of those flowering 

 plants which now constitute three-fourths of the living vege- 

 tation. The ferns of the Coal period had fewer rivals to com- 

 pete with, and more space in which to develope themselves 

 freely ; still, analogy would lead us to ascribe a luxuriant 

 growth of ferns, many of them arborescent, to a period when 



humidity 



The same 



may be said of the other vascular cryptogams which, together 

 with the ferns, form nineteen-twentieths of the carboniferous 

 flora. They belong to families allied to ferns, such for ex- 

 ample as the Sigillarise, Lepidodendra, and Calamites, and 

 most of them attained a vastly greater size, and had a more 

 complex structure, than any of their modern representatives. 

 Their stems had also a lax tissue and, like living cryptogams 

 of the same families, they must have derived the greater 

 part of the water which entered into their composition, as 

 well as their carbon, by their leaves from the air. They could 

















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