In view of these great and
admitted fluctuations of the earth's temperature one does not see
any reason for hesitating to admit a fall of temperature in the
Cretaceous, if the facts point to it.
On the other hand, the alternative suggestions are not very
convincing. We have noticed one of these suggestions in
connection with the origin of the Angiosperms. It hints that this
may be related to developments of the insect world. Most probably
the development of the characteristic flowers of the Angiosperms
is connected with an increasing relation to insects, but what we
want to understand especially is the deciduous character of their
leaves. Many of the Angiosperms are evergreen, so that it cannot
be said that the one change entailed the other. In fact, a
careful study of the leaves preserved in the rocks seems to show
the deciduous Angiosperms gaining on the evergreens at the end of
the Cretaceous. The most natural, it not the only, interpretation
of this is that the temperature is falling. Deciduous trees shed
their leaves so as to check their transpiration when a season
comes on in which they cannot absorb the normal amount of
moisture.
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