THE EVOLUTION OF THE PLANT-WORLD 15 



the general evolutionary advance. " The palaeobotanical 

 record is essentially the story of the successive ascendency 

 of a series of dominant families, each of which attained 

 its maximum in organisation as well as in extent, and 

 then sank into comparative obscurity, giving place to 

 other families which, under new conditions, were better 

 able to take a leading place. As each family ran its 

 downward course, its members either underwent an 

 actual reduction in structure as they became relegated 

 to herbaceous or, perhaps, aquatic life, . . . or the higher 

 branches of the family were crowded out altogether, 

 and only the 'poor relations' were able to maintain 

 their position by evading the competition of the 

 ascendant races." 1 



This succession of dominant groups was well tabulated 

 by Brongniart in 1849 as follows: 



III. Reign of Angiosperms { 



(4. Jurassic epoch (in- 

 II. Reign of Gymnosperms i eluding the Wealden) 



t 3 . Triassic epoch. 



T -o , * f 2. Permian epoch. 



I. Reign of Acrogens 1 , Carbonife] us epoc h. 



The flora of the Devonian age, the oldest known land 

 flora, described chiefly from North America, does not 

 differ very widely from that of the overlying Lower 

 Carboniferous. Not only does it include undoubted 

 horsetails, such as Avchcpocalamites; club-mosses, such 

 as Lepidodendron; and apparently true ferns, such as 

 Arch&opteris ; but also three or four generalised types 

 of great interest. 



In Upper Devonian rocks, in Bear Island in the 

 Arctic Ocean, a genus has been discovered known as 

 Pseudobornia. It was a large plant with a jointed 

 stem like Catamites, but with much -forked, divided, and 

 almost fern-like leaves in whorls of about four each. 

 In the same rocks, but also elsewhere and in more 

 modern beds of Carboniferous age, we have the better- 

 known genus Sphenophyllum, which is the type of a 

 distinct class of Pteridophyta. These were slender, 



1 D. H. Scott in Darwin and Modern Science (1909), pp. 202-3. 



