[Illustration: Fig. 113.--_Trigonocarpon ovatum_. Coal-measures,
Britain. (After Liudley and Hutton.)]
The _Lepidodendroids and Sigillaroids, though the first were
certainly, and the second possibly, Cryptogamic or flowerless
plants, must have constituted the main mass of the forests of
the Coal period; but we are not without evidence of the existence
at the same time of genuine "trees," in the technical sense of
this term--namely, flowering plants with large woody stems. So
far as is certainly known, all the true trees of the Carboniferous
formation were _Conifers_, allied to the existing Pines and Firs.
They are recognised by the great size and concentric woody rings
of their prostrate, rarely erect trunks, and by the presence
of disc-bearing fibres in their wood, as demonstrated by the
microscope; and the principal genera which have been recognised
are _Dadoxylon, Paloeoxylon, Araucarioxylon_, and _Pinites_.
Their fruit is not known with absolute certainty, unless it be
represented, as often conjectured, by _Trigonocarpon_ (fig. 113).
The fruits known under this name are nut-like, often of considerable
size, and commonly three- or six-angled. They probably originally
possessed a fleshy envelope; and if truly referable to the
_Conifers_, they would indicate that these ancient evergreens
produced berries instead of cones, and thus resembled the modern
Yews rather than Pines.
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