MANUAL OF NATURE STUDY. 
137 
the root point has developed roots and leaves suffi¬ 
cient for an independent existence of the fern 
plant, the prothallium withers away just as the 
seed leaves of a bean do under similar conditions. 
It will be seen, then, from the foregoing descrip¬ 
tion that the fern plant does not reproduce a fern 
plant immediately, as do beans, peas and other 
flowering plants; but that it first produces spores, 
the spores produce prothallia, and the prothallium 
in monoecious specimens gives rise to male and 
female organs, and finally these organs reproduce 
the fern plant, which again produces spores. Such 
a process is called alternation of generations. 
Mosses. 
Where do they grow ? On which side of tree do 
you find them most abundant ? On which side of 
rock? On which side of hill? If found on the 
south side of rock, tree or hill, what must necessar¬ 
ily be the other conditions? 
While examining the rocks and trees you will 
doubtless find a scaly-like plant that spreads out 
over the rock and sticks very closely to it. This 
plant is known as one species of lichen . Some 
people call it moss, but it is not true moss. You 
will find it quite plentifully distributed over the 
surface of old marble slabs in grave yards. After 
many, many years, perhaps centuries, the lichen 
