FERNS, FOSSILS AND FUEL 
must have developed along the water’s edge. These were 
plants which could live in water and could continue to 
exist in moist places where the sea had receded or the 
tide ebbed, in shore swamps that had been uncovered 
by the sea, or in the deltas of great rivers. Gradually 
life crept into the valleys, clinging first to moist and 
swampy places, and later reaching out to the uplands, 
until the narrow bands that had edged the water widened 
and covered the continents. 
How did these early land plants look? We can draw 
some conclusions from the oldest land plants we find in 
the Lower Devonian period. These plants already had 
attained a more or less advanced stage. They can be 
classified among the pteridophytes or fern types, although 
they are primitive and show many features of a moss 
or algalike character. 
The first land plants could only have originated from 
algae. They were probably composite types, which com¬ 
bined features of algae, mosses, and pteridophytes. We 
find that original types from which other types later de¬ 
velop nearly always combine the features of several groups. 
The types which develop from these primitive forms have 
specialized in one feature and have become rudimentary 
in all the other features. It is a progressive specialization 
which seems to have created new forms. 
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