l8o THE FAIRY-LAND OF SCIENCE. 
powdery dust a. These spores are full of resin, and 
they are collected on the Continent for making arti- 
ficial lightning in the theatres, because they flare when 
lighted. 
Now this little Selaginella is of all living plants the 
one most like some of the gigantic trees of the coal- 
forests. If you look at this picture of a coal-forest 
(Fig. 51), you will find it difficult perhaps to believe 
that those great trees, with diamond markings all up 
the trunk, hanging over from the right to the left of 
the picture, and covering all the top with their boughs, 
could be ki any way relations of the little Selaginella ; 
yet we find branches of them in the beds above the 
coal, bearing cones larger but just like Selaginella 
cones ; and what is most curious, the spores in these 
cones are of exactly the same kind and not any larger 
than those of the club-moss. 
These trees are called by botanists Lepidodendrons, 
or scaly trees ; there are numbers of them in all coal- 
mines, and one trunk has been found 49 feet long. 
Their branches were divided in a curious forked 
manner and bore cones at the ends. The spores 
which fell from these cones are found flattened in the 
coal, and they may be seen scattered about in the 
coal-ball (Fig. 49). 
Another famous tree which grew in the coal-forests 
was the one whose roots we found in the floor or 
underclay of the coal. It has been called Sigillaria, 
because it has marks like seals (sigillum, a seal) all 
up the trunk, due to the scars left by the leaves when 
they fell from the tree. You will see the Sigillarias 
on the left-hand side of the coal-forest picture, having 
those curious tufts of leaves springing out of them at 
