Australia.]
The _plants_ of the Trias are, on the whole, as distinctively
Mesozoic in their aspect as those of the Permian are Palaeozoic.
In spite, therefore, of the great difficulty which is experienced
in effecting a satisfactory stratigraphical separation between
the Permian and the Trias, we have in this fact a proof that the
two formations were divided by an interval of time sufficient
to allow of enormous changes in the terrestrial vegetation of the
world. The _Lepidodendroids, Asterophyllites_, and _Annularioe_,
of the Coal and Permian formations, have now apparently wholly
disappeared: and the Triassic flora consists mainly of Ferns,
Cycads, and Conifers, of which only the two last need special
notice. The _Cycads_ (fig. 140) are true exogenous plants, which
in general form and habit of growth present considerable resemblance
to young Palms, but which in reality are most nearly related to
the Pines and Firs (_Coniferoe_). The trunk is unbranched, often
much shortened, and bears a crown of feathery pinnate fronds.
The leaves are usually "circinate"--they unroll in expanding,
like the fronds of ferns. The seeds are not protected by a
seed-vessel, but are borne upon the edge of altered leaves, or
are carried on the scales of a cone. All the living species of
Cycads are natives of warm countries, such as South America, the
West Indies, Japan, Australia, Southern Asia, and South Africa.
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