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. The name _Micrococcus Guignardi_ has been applied to more or less spherical bodies 2·2µ in diameter, also met with in silicified plants. A portion of one of Renault’s figures is reproduced in Fig. 28 A. The faint and broken lines mark the position of the middle lamellae of parenchymatous cells from the pith of a Calamite. The tissue has been almost completely destroyed, but the more resistant middle lamellae have been partially preserved. The short and broad rods represent what Renault terms _Bacillus Tieghemi_; the small circle in the middle of some of these being referred to as a spore, and in one specimen shown in the figure, the second rod at right angles to the first is described as a small daughter-Bacillus formed by the germination of the central spore. The isolated circles in the figure are referred to _Micrococcus_. [Sidenote: FOSSIL BACTERIA.] It is unnecessary to give an account of the numerous examples of _Micrococci_ and _Bacilli_ described by Renault from Devonian, Carboniferous, Permian and Jurassic rocks. We may, however, in a few words consider the general question of the existence and possible determination of fossil Bacteria. In 1877 Prof. Van Tieghem[218] of Paris drew attention to the method of operation and plan of attack of _Bacillus amylobacter_ as a destructive agent in the decay of plant débris in water. He was able to follow the gradual disorganisation of the tissues and the various steps in the ‘butyric fermentation’ effected by this _Bacterium_. Similarly the same author[219] was able to detect the action of an allied organism in some silicified tissues from the Carboniferous nodules of Grand-Croix, a well-known locality for petrified plants near Saint-Étienne. He recognised also the traces of the _Bacillus_ itself in the partially destroyed plant tissues. The Palaeozoic Bacteria made use of some cellulose-dissolving ferment of which the action is clearly demonstrated in sections of silicified tissues. Many of the phenomena described by Renault and Bertrand as due to similar Bacterial action, afford additional evidence that the gradual disorganisation of vegetable tissues was effected in precisely the same manner as at the present day.