We are indebted to
Professor Heer, of Zurich, for the description, restoration, and classification
of several hundred species and varieties of these fossil plants, the whole of
which he has illustrated by excellent figures in his "Flora Tertiaria
Helvetiae." This great work, and those of Adolphe Brongniart, Unger, Goppert and
others, show that this class of fossils is beginning to play the same important
part in the classification of the tertiary strata containing lignite or brown
coal as an older flora has long played in enabling us to understand the ancient
coal or carboniferous formation. No small skepticism has always prevailed among
botanists as to whether the leaves alone and the wood of plants could ever
afford sufficient data for determining even genera and families in the vegetable
kingdom. In truth, before such remains could be rendered available a new science
had to be created. It was necessary to study the outlines, nervation, and
microscopic structure of the leaves, with a degree of care which had never been
called for in the classification of living plants, where the flower and fruit
afforded characters so much more definite and satisfactory.
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