Brongniart[464] first mentioned this fossil hepatic, which was found in the calcareous travertine of Sézanne of Oligocene age in the Province of Marne. The specimens figured by Saporta[465] show very clearly the characters of one of the Marchantiaceae, and in this case we have the additional evidence of the characteristic male receptacles which are given off from a point towards the apex of the lobes, and arise from a slight median depression. In one of Saporta’s figures (reproduced in fig. 50 A) there are represented some median scars which may mark the position of cups similar to those which occur on recent species of Marchantia, and in which gemmæ or bulbils are produced.
Fig. 50. Marchantites Sezannensis Sap. A. Surface view of the thallus; g, ? cups with gemmæ. B. A male branch. C. A portion of A magnified to show the surface features. (After Saporta.)
The collection of Sézanne fossils in the Sorbonne includes some very beautiful casts of Marchantites in which the structural details are preserved much more perfectly than in the examples described by Saporta. In a few specimens which Prof. Munier-Chalmas recently showed me the reproductive branches were exceedingly well shown. The fossils occur as moulds in the travertine, and the museum specimens are in the form of plaster-casts taken from the natural moulds.
Several species of Liverworts belonging to the Marchantiales and Jungermanniales have been recorded from the amber of North Germany, of Oligocene age. These appear to be represented by small fragments, such as are figured by Göppert and Berendt[466] in their monograph on the amber plants, published in 1845. The determinations have since been revised by Gottsche[467], who recognises species of Frullania, Jungermannia, and other genera.
| II. MUSCI. | SPHAGNALES. ANDREAEALES. BRYALES. |
The plant-body (gametophyte) in the Musci consists of a stem bearing thin leaves, usually spirally disposed, rarely in two rows. The internal differentiation of the stem is generally well marked, and in some cases is comparable in complexity with the structure of the higher plants. A protonema arises from the spore, having the form of a branched filamentous, or more rarely a thalloid structure. Reproduction as in the group Bryophyta.
Mosses like Liverworts have an extremely wide distribution, and occur in various habitats. In many districts vast tracts of country are practically monopolised by peat-forming genera, such as Sphagnum and other Mosses. Some genera are found on rocks at high altitudes in dry regions, a few grow as saprophytes, and many occur either as epiphytes on the leaves and stems of other plants, or carpeting the ground under the shade of forest trees.
DETERMINATION OF MOSSES.
In the simpler Mosses, the stem consists of a parenchymatous ground-tissue with a few outer layers of thicker-walled and smaller cells. In others there is a distinct central cylinder which occupies the axis of the stem, and consists of long and narrow cells; in the more complex forms the structure of the axial tissues suggests the central cylinder or stele of higher plants. The genus Polytrichum, so abundant on English moors, illustrates this higher type of stem differentiation. In a transverse section of the stem the peripheral tissue is seen to be composed of thick-walled cells, passing internally into large parenchymatous tissue. The axial part is occupied by a definite central cylinder consisting in the centre of elongated elements with dark-coloured and thick walls having thin transverse septa; surrounding this central tissue there are thinner walled elements, of which some closely agree in form with the sieve-tubes of the higher plants. The central tissue may be regarded as a rudimentary type of xylem, and the surrounding tissue as a rudimentary phloem. Each leaf is traversed by a median conducting strand which passes into the stem and eventually becomes connected with the axial cylinder.