122 



Biology in America 



forming period, and which, from their abundance and that of 

 the giant club mosses, is known as the "age of amphibians 

 and lycopods." 



The modern club moss is an inconspicuous humble plant, 

 usually creeping upon the ground in the forest, and covered 

 with small pointed leaves. It is most familiar to us in the 

 decorations of the Christmas time. But the club mosses which 

 we burn today as coal, were princely trees in the carboniferous 



FOOTPRINT OF A PRIMITIVE AMPHIBIAN 

 Courtesy of Professor R. 8. Lull. 



forests, one hundred feet in height and five to six feet in 

 diameter. Associated with them along the borders of lake 

 and pond were giant forerunners of our "horse tail ferns," 

 slender plants, sixty to one hundred feet in height, though 

 but one or two feet in diameter. Their descendants of the 

 present are for the most part only a few feet in height, 

 though a few of the South American forms may reach thirty 

 or forty feet. 



During the Carboniferous period, when the earth 's surface 

 was covered by vast swamps, wherein the decaying vegeta- 



