to-day are known. The
sequoias (the giant Californian trees) still represent the conifers in
great abundance, with the eucalyptus and other plants that are now found
only much further south. The ginkgoes struggle on for a time. The cycads
dwindle enormously. Of 700 specimens in one early Cretaceous deposit
only 96 are Angiosperms; of 460 species in a later deposit about 400 are
Angiosperms. They oust the cycads in Europe and America, as the cycads
and conifers had ousted the Cryptogams. The change in the face of the
earth would be remarkable. Instead of the groves of palm-like cycads,
with their large and flower-like fructifications, above which the pines
and firs and cypresses reared their sombre forms, there were now forests
of delicate-leaved maples, beeches, and oaks, bearing nutritious fruit
for the coming race of animals. Grasses also and palms begin in the
Cretaceous; though the grasses would at first be coarse and isolated
tufts. Even flowers, of the lily family (apparently), are still detected
in the crushed and petrified remains.

We will give some consideration later to the evolution of the
Angiosperms. For the moment it is chiefly important to notice a feature
of them to which the botanist pays less attention. In his technical view
the Angiosperm is distinguished by the structure of its reproductive
apparatus, its flowers, and some recent botanists wonder whether the
key to this expansion of the flowering plants may not be found in a
development of the insect world and of its relation to vegetation. In
point of fact, we have no geological indication of any great development
of the insects until the Tertiary Era, when we shall find them deploying
into a vast army and producing their highest types. In any case, such
a view leaves wholly unexplained the feature of the Angiosperms which
chiefly concerns us. This is that most of them shed the whole of their
leaves periodically, as the winter approaches. No such trees had yet
been known on the earth. All trees hitherto had been evergreen, and we
need a specific and adequate explanation why the earth is now covered,
in the northern region, with forests of trees which show naked boughs
and branches during a part of the year.

The majority of palaeontologists conclude at once, and quite
confidently, from this rise and spread of the deciduous trees, that a
winter season has at length set in on the earth, and that this new type
of vegetation appears in response to an