170 THE GEOLOGICAL HISTORY OF PLANTS. 



1. That the aerial stems of ordinary Calamites had a thin cortical 

 layer, with Iacuna3 and fibrous bundles and -multiporous vessels. the 

 whole not differing much from the structure of modern Equiseta. 



2. Certain arborescent forms, perhaps allied to the true Calamites, 

 as well as possibly the old underground stems of ordinary species,* 

 assumed a thick-walled character in which the tissues resembled the 

 wedges of an exogen, and abundance of pseudo-scalarif orm fibres were 

 developed, while the ribbing of the external surface became obsolete 

 or was replaced by a mere irregular wrinkling. 



3. Sufficient discrimination has not been exercised in separating 

 casts of the internal cavities of Calamites and Calamodendron from 

 those representing other surfaces and the proper external surface. 



4. There is no excuse for attributing to Calamites the foliage of 

 Annularia, Asterophyllites, and Sphenophyllum, since these leaves 

 have not been found attached to true Calamite stems, and since the 

 structure of the stems of Asterophyllites as described by Williamson, 

 and that of Sphenophyllum as described by the writer, f are essen- 

 tially different from those of Calamites. 



5L As the species above described indicates, good external char- 

 acters can be found for establishing species of this genus, and these 

 species are of value as marks of geological age. 



O-enus ARCHSOCALAMITES, Sternberg. 



This genus has been established to include certain Calamites of 

 the Devonian and Lower Carboniferous, in which the furrows on the 

 stem do not alternate at the nodes or joints, and the leaves in one 

 species at least bifurcate. C. radiatus, Brongniart, is the typical 

 species. In North America it occurs in the Erian, probably as low 

 as the Middle Erian. In Europe it has so far been recognised in the 

 Lower Carboniferous only. I have, however, seen stems from alleged 

 Devonian beds in Devonshire which may have belonged to this species. 



Family ASTEROPHYLLITES ; Genus ASTEROPHYLLITES, Brongniart. 



Stems ribbed and jointed like the Calamites, but with inflated 

 nodes and a stout internal woody cylinder, which has been described 

 by Williamson. From the joints proceeded whorls of leaves or of 

 branchlets, bearing leaves which differed from those of Calamites in 

 their having a distinct middle rib or vein. The fructification con- 



* Williamson, " Transactions of the Royal Society.' 71 MeNab, in 

 " Proceedings of the Edinburgh Botanical Society." 

 f "Journal of the Geological Society," 1866. 



