-------------------------------------------------------

------------
|   (M.A.  Brongniart).          |                     |(Lindley). |
|CELLULAR                       |                     |           |
| Cryptogams (Flowerless)     |Fungi, seaweeds,     |Thallogens |
|                               |  lichens            |           |
|                               |                     |           |
|VASCULAR                       |                     |           |
| Cryptogams (Flowerless)     |Ferns, equisetums,   |Acrogens   |
|                               |  mosses, lycopodiums|           |
| Phanerogams (Flowering)     |                     |           |
|     Gymnosperms (having       |Conifers and         |Gymnogens  |
|        naked seeds)           |  cycads             |           |
|     Two or more Cotyledons    |                     |           |
|     Angiosperms (having       |                     |           |
|        enclosed seeds)        |                     |           |
|     Monocotyledons            |Palms, lilies,       |Endogens   |
|                               |  grasses            |           |
|     Dicotyledons              |Most European        |Exogens    |
|                               |  trees and shrubs   |           |
------------------------------------------------------------

-------

Adolphe Brongniart termed the coal era the “Age of Acrogens,” because, as we shall see, of the great predominance in those times of vascular cryptogamic plants, known in Dr Lindley’s nomenclature as “Acrogens.”

[Illustration:  FIG. 10.—­Spenophyllum cuneifolium. Coal-shale.]

Two of these families have already been dealt with, viz., the ferns (felices), and the equisetums, (calamites and equisetites), and we now have to pass on to another family.  This is that which includes the fossil representatives of the Lycopodiums, or Club-mosses, and which goes to make up in some coals as much as two-thirds of the whole mass.  Everyone is more or less familiar with some of the living Lycopodiums, those delicate little fern-like mosses which are to be found in many a home.  They are but lowly members of our British flora, and it may seem somewhat astounding at first sight that their remote ancestors occupied so important a position in the forests of the ancient period of which we are speaking.  Some two hundred living species are known, most of them being confined to tropical climates.  They are as a rule, low creeping plants, although some few stand erect.  There is room for astonishment when we consider the fact that the fossil representatives of the family, known as Lepidodendra, attained a height of no less than fifty feet, and, there is good ground for believing, in many cases, a far greater magnitude.  They consist of long straight stems, or trunks which branch considerably near the top.  These stems are covered with scars or scales, which have been caused by the separation of the petioles or leaf-stalks, and this gives rise to the name which the genus bears.  The scars are arranged in a spiral manner the whole of the way up the stem, and the stems often remain perfectly upright in the coal-mines, and reach into the strata which have accumulated above the coal-seam.