Our attention will be concentrated on the following questions, all relating
to the phylogeny of main groups of plants: i. The Origin of the
Angiosperms. ii. The Origin of the Seed-plants. iii. The Origin of the
different classes of the Higher Cryptogamia.

i. THE ORIGIN OF THE ANGIOSPERMS.

The first of these questions has long been the great crux of botanical
phylogeny, and until quite recently no light had been thrown upon the
difficulty. The Angiosperms are the Flowering Plants, par excellence, and
form, beyond comparison, the dominant sub-kingdom in the flora of our own
age, including, apart from a few Conifers and Ferns, all the most familiar
plants of our fields and gardens, and practically all plants of service to
man. All recent work has tended to separate the Angiosperms more widely
from the other seed-plants now living, the Gymnosperms. Vast as is the
range of organisation presented by the great modern sub-kingdom, embracing
forms adapted to every environment, there is yet a marked uniformity in
certain points of structure, as in the development of the embryo-sac and
its contents, the pollination through the intervention of a stigma, the
strange phenomenon of double fertilisation (One sperm fertilising the egg,
while the other unites with the embryo-sac nucleus, itself the product of a
nuclear fusion, to give rise to a nutritive tissue, the endosperm.), the
structure of the stamens, and the arrangement of the parts of the flower.
All these points are common to Monocotyledons and Dicotyledons, and
separate the Angiosperms collectively from all other plants.

In geological history the Angiosperms first appear in the Lower Cretaceous,
and by Upper Cretaceous times had already swamped all other vegetation and
seized the dominant position which they still hold. Thus they are isolated
structurally from the rest of the Vegetable Kingdom, while historically