646 GEOLOGY 



bearing plants, though ferns were probably present. The ferns 

 are a strangely persistent type. Species still live which, so far as 

 outer form is concerned, might be referred to Carboniferous genera; 

 yet under this general similarity of form, there have been notable 

 changes of structure and function. They seem to have been, even 

 at this early time, thoroughly differentiated from other plants. 



The Equisetales (calamites, horsetails). These plants, repre- 

 sented now by a single genus (Equisetum) , were an important mem- 

 ber of the Carboniferous flora. The calamites were not only larger, 

 but more highly organized than the modern representatives of this 

 group. The largest tropical forms of to-day have slender stems 30 

 or 40 feet long, whereas the Carboniferous calamites reached a foot 

 or two in diameter and probably 60 to 90 feet in height. They had 

 hollow stems, or a core of pith only, and casts of the interior are 

 common fossils. Branches from the main trunk were comparatively 

 few, and in whorls. The leaves also were in whorls (Fig. 447) and 

 dwarfed, though not so much so as in the modern type, in which 

 the leaves have almost disappeared. The structure of the leaves 

 was of the type adapted to dry weather (xerophytic) as in the pine 

 and in many desert plants, and also, contradictorily enough, as in 

 some undrained swamp plants. The root structure was of the type 

 commonly found under water or in wet mud, and the calamites 

 probably frequented swamps and lowlands. The calamites were 

 probably associated in thickets and jungles of cane-brake or bain- 

 boo type. Their history may run far back, as they were well differ- 

 entiated -in the Devonian. Their ancestry is uncertain, but the 

 next group throws light on their relations. 



The Sphenophyllales. Recent studies have shown that the 

 graceful, slender plants with whorled leaves, referred to the genus 

 Sphenophijllum (c, Fig. 449), and formerly classed as calami* es. 

 should be made a class by themselves. Their importance lies chiefly 

 in the fact that while they have certain ralamarian features, they 

 have others possessed by the lycopods. This is interpreted to mean 

 that these two groups (calamarians and lycopods, p. 944) were 

 united with the Sphenophi/llales in a common ancestral form. 1 

 The stems were long, slender, and apparently weak, and a climbing 



1 Seward, Fossil Plants, p. 413; Scott, Studies in Fossil Botany, p. I'.M 



