392 PART IV. VEGETABLE TAXONOMY. 



were the slender-stemmed Protannularias and Sphenophyllums, 

 having their leaves arranged in whorls. Their affinities have 

 not yet been definitely settled, but they are supposed to have 

 been related to the Rhizocarpea?. The Psilophytons, with their 

 gracefully coiled branches and fern-like habits, must have formed 

 a dense undergrowth. They were related to the modern Psilo- 

 tums. But the Nematophytons, some of which attained tree-like 

 dimensions, were apparently the giants of those primeval forests. 

 They were strange plants, of peculiar structure, and uncertain 

 affinities, in some respects resembling huge Fucaceae, in others, 

 Gymnosperms, but also differing in important particulars from 

 both. 



But the terrestrial species were still few in number ; land 

 vegetation yet held but a subordinate place in the world's flora. 



In the Devonian the species of land-plants became much 

 more abundant, and more highly developed forms were intro- 

 duced. About one hundred and eighty different species belong- 

 ing to this period have been described. Among them are found 

 representatives of all the great groups of the Pteridophyta, and 

 a few Gymnosperms. The Equisetinea^ are represented by the 

 Asterophyllites, with their star-like whorls of leaves and jointed 

 stems, and the Calamites, which resembled our modern Horse- 

 tails, only that they grew to much larger size, and had a more 

 complex stem-structure. The Filicinea^ were represented by 

 various species of Ferns, all differing from our modern species. 

 The Lycopodinea were still represented by Psilophytons, which 

 continued in great abundance, but Lepidodendrons and Sigillar- 

 ias, huge, tree-like Club-Mosses, but having affinities also with 

 Gymnosperms, are introduced, and constitute a conspicuous part 

 of the forest vegetation of the age. The Gymnosperms are 

 represented by the strange Dadoxylons and Cordaites, quite 

 different from, but clearly forecasting, our modern Conifers. 



But the land flora of the Devonian, rich as it is, is poor in 

 comparison to that of the great coal or Carboniferous age which 

 immediately succeeds it. Nearly two thousand species belong- 

 ing to this age have been described. The plants, though largely 

 of the same types, are not only much more numerous in individ- 

 uals and varied in species, but the old species and many of the 

 old genera are gone and new ones have taken their place. Lepi- 



