THE CARBONIFEROUS PERIODS 



495 



stouter, one specimen six feet 

 in diameter and 18 feet high 

 having been described. 



The fruit of both the Lepido- 

 dendron and Sigillaria was in 

 the form of well-defined cones 

 that were usually borne at the 

 ends of the smaller branches. In 

 the clay underlying coal seams 

 the " roots " or underground 

 stems of the lycopods often 

 occur and are called Stigmaria. 



The trunks of the lycopods 

 consisted of a hard, woody rind 

 and a soft, cellular interior which 

 quickly decayed. As a result 

 of this structure the fossil trunks 

 seldom show their original cy- L FlG - 473- - Bark of Sigillaria, showing 

 .. . . . r . the vertical arrangement or the leaves and 



Iindrical form, but are usually tne fl ute d surface. 



flattened into thin sheets. 



The great lycopods of the Carboniferous are now represented by 



the insignificant ground pine and Selaginella. 



The coal beds of the Carboniferous are 

 largely composed of Lepidodendron and Sigil- 

 laria remains. Some coal of this period 

 (cannel), however, is made up chiefly of 

 spores of Carboniferous plants. 



(4) Sphenophylls. — This extinct group is 

 interesting because it suggests a common an- 

 cestor for the lycopods and horsetails (Equi- 

 setales). The plant had a slender, ribbed stem, 

 seldom more than a quarter of an inch in 

 diameter, which bore delicate, wedge-shaped 

 leaves (Fig. 474) attached in whorls to the 

 stem by their ends. Sometimes the leaves 

 were deeply cut, making them almost hairlike 



fifths of an inch in in appearance. These plants probably had a 



diameter. The spheno- tra iK n g habit, or perhaps supported themselves 



phyllums probably sup- r r rr 



ported themselves by on stronger plants. Sphenophylls bore cones 



limbing. somewhat like those of the Calamites. 



CLELAND GEOL. — $2 



U^§^» 



Fig. 474. — Stem and 

 leaves of Sphenophyllum, 

 a slender plant, the stem 

 seldom exceeding two 



