Origin of Angiosperms 205 
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 inter- 
vention of a stigma, the strange phenomenon of double fertilisation’, 
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 they suddenly appear, almost 
in full force, and apparently without intermediaries with other groups. 
To quote Darwin’s vigorous words: “The rapid development, as far 
as we can judge, of all the higher plants within recent geological 
times is an abominable mystery”.” A couple of years later he made 
a bold suggestion (which he only called an “idle thought”) to meet 
this difficulty. He says: “I have been so astonished at the appa- 
rently sudden coming in of the higher phanerogams, that I have 
sometimes fancied that development might have slowly gone on for 
an immense period in some isolated continent or large island, perhaps 
near the South Pole*®.” This idea of an Angiospermous invasion from 
some lost southern land has sometimes been revived since, but has 
not, so far as the writer is aware, been supported by evidence. Light 
on the problem has come from a different direction. 
The immense development of plants with the habit of Cycads, 
during the Mesozoic Period up to the Lower Cretaceous, has long 
been known. The existing Order Cycadaceae is a small family, with 
9 genera and perhaps 100 species, occurring in the tropical and 
sub-tropical zones of both the Old and New World, but nowhere 
forming a dominant feature in the vegetation. Some few attain the 
stature of small trees, while in the majority the stem is short, though 
often living to a great age. The large pinnate or rarely bipinnate 
1 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. 
? More Letters of Charles Darwin, Vol. 1. p. 20, letter to J. D, Hooker, 1879. 
3 Ibid. p. 26, letter to Hooker, 1881, 
all 
