FERNS, FOSSILS AND FUEL 
Musci or true mosses. Among the true mosses we find 
a development of stems and leaves on a primitive scale. 
Their tiny stems, however, do not have a system of 
woody fibers. They are formed merely of longitudinally 
stretched cells. The leaves of the mosses have the shape 
of higher plant leaves, but consist of single layers of cells. 
All the mosses have a distinct alternation of sexual 
and asexual reproduction. The algae may reproduce 
non-sexually by spores only which germinate and grow 
into a new plant, or they may have an alternation of 
sexual and non-sexual reproduction as in the mosses. In 
the bryophytes the spores, which we can see in tiny cap¬ 
sules on mosses, germinate into small threads of cells 
from which the adult moss plant develops. The adult 
plant has small female egg cells, and male sex cells con¬ 
taining spermatazoa, which move to the egg cells and 
fertilize them. Out of the fertilized egg cell grows a 
capsule-like organ which contains spores, but which re¬ 
mains connected with the plant having the sex organs. 
The third great stem is that of the pteridophytes, or 
ferns and fern allies. They are the most highly developed 
of all the spore-bearing plants and include such types 
as the horse-tails (equisetales), club mosses (lycopo- 
diales), and true ferns (filicales). They, too, have an 
alternation of sexual and asexual reproduction. A spore 
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