138 
MANUAL OF NATURE STUDY. 
causes the rock to decay and crumble into dust or soil, 
sufficient to give the moss-spores lodgment. So moss 
takes the place of lichens j ust as soon as the latter has 
prepared the soil for the support of the moss forest. 
But moss will grow upon damp soil, wherever shaded 
and supplied with proper amount of heat. In fact, 
it does not require a great deal of heat or moisture 
to support some kinds of moss, as it is well known 
that great quantities of moss grow in the cold re¬ 
gions of the north where few other plants can exist. 
It will also do well upon dry knolls. Let the child¬ 
ren state where they have seen moss, and name 
some things peculiar to its nature. The Pigeon- 
Wheat moss is perhaps the commonest kind and 
can be found in great abundance by the children 
upon almost any side hill and often between the 
bricks of walks where the place is damp and shaded. 
The Pigeon-Wheat moss is known by its long 
pedicel bearing on its apex a capsule containing 
spores which, when ripe, are thrown out to be 
scattered by the wind the same as fern spores. 
These spores are no more the nature of seeds 
than fern spores are seeds, or puff-ball dust is seed. 
All seeds contain an embryo and food supper, the 
latter being either within or without the embryo; 
but the spores contain no'embryo. They give 
rise to green web-like threads, called protonema, 
which have no roots, but cling very closely 
