122 



THE GEOLOGICAL HISTORY OF PLANTS. 



son, of Manchester, to illustrate the structure of Cala- 

 mites, and he has shown that these plants, like other 

 cryptogams of the Carboniferous, had mostly stems with 

 regular fibrous wedges, like those of exogens. The 

 structure of the stem is, indeed, so complex, and differs 

 so much in different stages of growth, and different states 

 of preservation, that we are in danger of falling into the 

 greatest confusion in classifying these plants. Sometimes 

 what we call a Calamite is a mere cast of its pith showing 

 longitudinal striae and constrictions at the nodes. Some- 



Fio. 45.— Aster >op7iylHies, Sphenophyllum, and Annularia. a, Astero- 

 pTiyllites trinerne. a 1 , Leaf enlarged, b, Annularia sphenophylloides. 

 b 1 , Leaf enlarged, c, Sphenophyllum erosum. c 1 , Leaflet enlarged. 

 c 2 , Scalariform vessel of Sphenophyllum. d, Pinnularia ramosissima, 

 probably a root. 



times we have the form of the outer surface of the woody 

 cylinder, showing longitudinal ribs, nodes, and marks of 

 the emission of the branchlets. Sometimes we have the 

 outer surface of the plant covered with a smooth bark 

 showing flat ribs, or almost smooth, and having at the 

 nodes regular articulations with the bases of the verticil- 



