FERNS, FOSSILS AND FUEL 
Neuropteris, and the Alethopteris, whose leaflets formed 
elegant little curves. Another, the Odontopteris, had 
tooth-shaped leaflets, while the Callipteridium, meaning 
the beautiful fern, had oblong leaflets with delicate ven¬ 
ation. There was a water plant called Sphenophyllum, 
which is now entirely extinct. Its branches drifted in 
the water and bore whorls of wedge-shaped leaves in 
multiples of three, usually having nine leaves to a whorl. 
At the ends of its stems were spikes with whorls of 
spore-capsules. 
The giants of the forests were the big club-moss plants 
(lycopods), which were trees sometimes one hundred 
feet high and with trunks three or four feet in diameter. 
The stems or trunks were forked and had tufts of grass¬ 
like leaves at the ends of the branches. They all bore 
large cones filled with innumerable spores. The bark 
of these great lycopods resembled an alligator’s skin. 
Some had rhomboid impressions arranged in spirals and 
this type was called Lepidodendron, which means scale- 
tree. Others had rows of hexagonal or round impressions 
which resembled the wax seals formerly used to close 
letters. This type was called Sigillaria. In addition to 
these, there was a great variety of other lycopod types. 
The ornamentation of the bark is used as the principal 
character for establishing subgenera and species. 
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