| SERIES. | FORMS FOUND FOSSIL. | |
| I.— | THALLOPHYTA | Sea-weeds: as Corallines and Calcareous Algae. |
| II.— | BRYOPHYTA | Mosses, Liverworts. |
| III.— | PTERIDOPHYTA | Fern-like plants, as Horse-tails, Club-mosses and true Ferns. |
| IV.— | PTERIDOSPERMEAE | Oldest Seed-bearing plants, with fern-like foliage. |
| V.— | GYMNOSPERMEAE | Plants with naked seeds, as Cycads (Fern-palms), Ginkgo (Maiden-hair Tree), and Conifers (Pine trees). |
| VI.— | ANGIOSPERMEAE | Flowering plants, as Grasses, Lilies and all ordinary trees and plants. |
Characters of the Plant Series.
THALLOPHYTA.—
The first series, the Thallophytes, are simple unicellular plants, and occupy the same position in the vegetable kingdom as the Protozoa do in the animal kingdom. Fossil remains of these organisms seem to be fairly well distributed throughout the entire geological series, but, owing to the soft structure of the fronds in most of the types, it is often a matter of doubt whether we are dealing with a true thallophyte or not. Many of the so-called sea-weeds (fucoids) may be only trails or markings left by other organisms, as shell-fish and crustaceans.
BRYOPHYTA.—
The second series, the Bryophytes or moss plants, are represented in the fossil state by a few unimportant examples.
PTERIDOPHYTA.—
The third series, the Pteridophytes, includes the Ferns found from the Devonian up to the present day, Horse-tails and allied forms, like Equisetites, and the Club-mosses and Lepidodendron of the Carboniferous period in various parts of the world.
PTERIDOSPERMEAE.—