A PIECE OF COAL. 185 
earth away from the coal and keep it pure. This plant 
was a near relation of the " horsetail," or Equisetum, 
which grows in our marshes; only, just as in the case 
of the other trees, it was enormously larger, being 
often 20 feet high, whereas the little Equisetum, Fig. 
54, is seldom more than a foot, and never more than 6 
feet high in North America, though in tropical South 
America they are much higher. Still, if you have ever 
gathered " horsetails," you will see at once that those 
trees in the foreground of the picture (Fig. 53), with 
leaves arranged in stars round the branches, are only 
larger copies of the little marsh-plant; and the 
seed-vessels of the two plants are almost exactly the 
same. 
These great trees, the Lepidodendrons, the Sigil- 
larias, and the Calamites, together with large tree- 
ferns and 'smaller ferns, are the chief plants that we 
know of in the coal-forests. It seems very strange at 
first that they should have been so large when their 
descendants are now so small, but if you look at our 
chief plants and trees now, you will find that nearly 
all of them bear flowers, and this is a great advantage 
to them, because it tempts the insects to bring them 
the pollen-dust, as we saw in the last lecture. 
Now the Lepidodendrons and their companions 
had no true flowers, but only these seed-cases which 
we have mentioned; but as there were no flowering 
plants in their time, and they had the ground all to 
themselves, they grew fine and large. By-and-by, 
however, when the flowering plants came in, these be- 
gan to crowd out the old giants of the coal-forests, so 
that they dwindled and dwindled from century to cen- 
