The past history of plants by no means shows a regular progression from the
simple to the complex, but often the contrary. This apparent anomaly is
due to two causes.

1. The palaeobotanical record is essentially the story of the successive
ascendancy of a series of dominant families, each of which attained its
maximum, in organisation as well as in extent, and then sank into
comparative obscurity, giving place to other families, which under new
conditions were better able to take a leading place. As each family ran
its downward course, either its members underwent an actual reduction in
structure as they became relegated to herbaceous or perhaps aquatic life
(this may have happened with the Horsetails and with Isoetes if derived
from Lepidodendreae), or the higher branches of the family were crowded out
altogether and only the "poor relations" were able to maintain their
position by evading the competition of the ascendant races; this is also
illustrated by the history of the Lycopod phylum. In either case there
would result a lowering of the type of organisation within the group.

2. The course of real progress is often from the complex to the simple.
If, as we shall find some grounds for believing, the Angiosperms came from
a type with a flower resembling in its complexity that of Mesozoic
"Cycads," almost the whole evolution of the flower in the highest plants
has been a process of reduction. The stamen, in particular, has
undoubtedly become extremely simplified during evolution; in the most
primitive known seed-plants it was a highly compound leaf or pinna; its
reduction has gone on in the Conifers and modern Cycads, as well as in the
Angiosperms, though in different ways and to a varying extent.

The seed offers another striking example; the Palaeozoic seeds (if we leave