THE PENNSYLVANIAN PERIOD 



171 



feet or more and a diameter of 5 or 6 feet. The trunk seldom 

 branched and it ended with a rounded tip. In other respects these 

 trees were much like the Lepidodendrons. 



Equisetce ("Horse-tail" plants) were also common in the Penn- 

 sylvanian forests. These plants had long, slender, segmented 

 stems which were either hollow or filled with a large, soft pith 



Fig. 99 

 Fronds of a Pennsylvanian Fern, Mariopteris. (After D. White, U. S. Geo- 

 logical Survey, Monograph 37.) 



(Fig. 101). The leaves, which were arranged in whorls around the 

 stems at the joints, were of variable shapes and sizes, usually either 

 needle-like, scale-like, or strap-like. The outside of the stem had a 

 sort of finely fluted structure but without scars and not continuous 

 as in the Sigillarians. They reached heights of 60 to 90 feet and 

 diameters of 1 or 2 feet. Equisetae are today chiefly represented 

 by only a few species of rush-like forms not over a few feet high, 

 though in South America some very slender forms grow to heights 

 of 30 or 40 feet. 



