The paper-coal of Toula, which in some places reaches a thickness of 20 cm., is a plant-bed of exceptional interest. It differs from ordinary coal in being made up of numberless thin brown-papery sheets associated with a darker coloured substance largely composed of ulmic acid. Prof. Zeiller[211], in an interesting account of the papery layers, has shown that they consist of the cuticles of a Lepidodendroid plant, Bothrodendron. An examination of a piece of one of the sheets at once reveals the existence of a regular network of which the walls of the meshes are the outlines of the epidermal cells, the meshes being bridged across by a thin light brown membrane which represents the layer of cuticularised cell-wall of each epidermal cell. At regular intervals and disposed in a spiral arrangement, we find small gaps in the papery cuticle which mark the position of the Bothrodendron leaves. These Palaeozoic cuticles are not petrified; they are only slightly altered, and have retained the power of swelling in water, being able to take up stains like recent tissues. It may reasonably be assumed that the persistent cuticles owe their preservation to a greater power of resistance to destructive agents than was possessed by the other tissues of the plant. It is by no means unlikely, as Renault[212] has recently suggested, that as the Bothrodendron stem-fragments lay in the swamps or marshes the tissues were gradually eaten away by Bacteria, but the cuticles successfully resisted the attacks of the bacterial saprophytes. The same observer has described what he regards as the actual organism which effected this wholesale destruction, under the name Micrococcus Zeilleri. He finds, after treating the cuticles with ammonia to remove the ulmic acid, that there occur numerous minute spherical bodies, each surrounded by a thin envelope, either singly or in groups on the surface of the cuticular membrane. These vary in size from ·5µ to 1µ in diameter. I have not been able to detect any satisfactory proof of such Micrococci in specimens of the paper-coal which were treated according to Renault’s method, but it is extremely probable that this unusual method of preservation of stem-cuticles is the result of selective bacterial action.
Renault believes that some of the minute spherulitic structures which are seen in sections of decayed tissues of Palaeozoic plants owe their origin, in part, to the ravages of bacteria. The disorganisation of parenchymatous cells gives rise to a gelatinous substance in which needle-like crystals of silica may be deposited, from a siliceous solution, in a matrix which has resulted from bacterial activity. In some of the sections of tissues figured by Renault[213] the outlines of a few cells are still indicated by fragments of the partially decayed wall, while in other cells the walls have been completely destroyed by Bacteria of which some are preserved in the centre of the cell-area, forming a kind of nucleus to the siliceous spherulites.
BACILLI.
In addition to the Micrococcus described by Renault from the Toula paper-coal, there are a host of other forms which have been minutely diagnosed and figured by Profs. Renault and Bertrand[214]. These authors have discovered what they believe to be well-defined species of Micrococcus and Bacillus ranging in age from Devonian to Jurassic. The material which has afforded the somewhat startling results of their investigations consists partly of the coprolites of reptiles and fishes, and of silicified and calcified plant tissues.
Bacillus Permicus. Ren. and Bert.[215] (Fig. 28 B.)
This Bacillus, which was discovered in sections of a Permian coprolite from Central France, has the form of cylindrical rods 12–14µ in length, and 1·3–1·5µ broad, rounded at each end. The rods occur either singly or occasionally, two or three individuals are joined end to end. Fig. 28 B represents a piece of one of Renault and Bertrand’s sections; the small rods are clearly seen lying in various directions in the homogeneous matrix of the coprolite. Each individual is said to be surrounded by an extremely minute empty space ·4µ in width, originally occupied by the Bacillus membrane, the central rod representing the mineralised cell-contents. In this example the petrifying substance was probably derived from the phosphate of calcium of bones which were attacked by Bacteria. I am indebted to Prof. Renault for an opportunity of examining specimens of this and other fossil Bacteria, and in this particular case there is undoubtedly strong evidence in favour of the author’s determination.
Fig. 28. A, Bacillus Tieghemi Ren. and Micrococcus Guignardi Ren. B, Bacillus Permicus Ren. (After Renault.)
Bacillus Tieghemi Ren.[216] and Micrococcus Guignardi Ren.[217] (Fig. 28 A.)
Renault has given the name Bacillus Tieghemi to certain minute rods 6–10µ, in length, and 2·2–3·8µ broad, often containing a dark coloured spherical spore-like body 2µ in diameter, which have been found in the tissues of a Coal-Measure plant.