On the other hand, they approached
the ferns so much more closely than modern cycads do that it is often
impossible to say whether Jurassic remains must be classed as ferns or
cycads.

We have here, therefore, a most interesting evolutionary group. The
botanist finds even more difficulty than the zoologist in drawing up the
pedigrees of his plants, but the general features of the larger groups
which he finds in succession in the chronicle of the earth point very
decisively to evolution. The seed-bearing ferns of the Coal-forest point
upward to the later stage, and downward to a common origin with the
ordinary spore-bearing ferns. Some of them are "altogether of a
cycadean type" (Scott) in respect of the seed. On the other hand, the
Bennettiteae of the Jurassic have the mixed characters of ferns, cycads,
and flowering plants, and thus, in their turn, point downward to a lower
ancestry and upward to the next great stage in plant-development. It
is not suggested that the seed-ferns we know evolved into the cycads we
know, and these in turn into our flowering plants. It is enough for the
student of evolution to see in them so many stages in the evolution of
plants up to the Angiosperm level. The gaps between the various groups
are less rigid than scientific men used to think.

Taller than the cycads, firmer in the structure of the wood, and
destined to survive in thousands of species when the cycads would be
reduced to a hundred, were the pines and yews and other conifers of the
Jurassic landscape. We saw them first appearing, in the stunted Walchias
and Voltzias, during the severe conditions of the Permian period. Like
the birds and mammals they await the coming of a fresh period of cold
to give them a decided superiority over the cycads. Botanists look
for their ancestors in some form related to the Cordaites of the
Coal-forest. The ginkgo trees seem to be even more closely related to
the Cordaites, and evolved from an early and generalised branch of that
group. The Cordaites, we may recall, more or less united in one tree
the characters of the conifer (in their wood) and the cycad (in their
fruit).

So much for the evolutionary aspect of the Jurassic vegetation in
itself. Slender as the connecting links are, it points clearly enough
to a selection of higher types during the Permian revolution from
the varied mass of the Carboniferous flora, and it offers in turn a
singularly varied and rich group from which a fresh se