VII] BACTERIA. 133 



Bacteria, and their extraordinary power of successfully resisting 

 the most unfavourable conditions, render it probable that they 

 constitute an extremely ancient group of organisms. 



The wonderful perfection of preservation of many fossil 

 plants enables us to investigate the contents of petrified cells 

 and to examine in minutest detail the histology of extinct 

 plants. To those who are familiar with the possibilities of 

 microscopical research as applied to silicified and calcified 

 fossil tissues, it is by no means incredible that evidence has been 

 detected of the existence of Bacteria as far back in the history 

 of the earth as the Carboniferous and Devonian periods. 



Were there no trustworthy records of the occurrence of Bac- 

 teria in Palaeozoic times, it would still be a natural supposition 

 that these ubiquitous organisms must have been abundantly 

 represented. It has been suggested as a probable conclusion that 

 some forms of Bacteria, which produced chemical changes in the 

 soil necessary for the nutrition of plants, must have existed 

 contemporaneously with the oldest vegetation'. 



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^ in an interesting 

 account of the papery layers, has shown that they consist of the 

 cuticles of a Lepidodendroid plant, Boihrodendron. An exami- 

 nation 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 

 Boihrodendron leaves. These Palaeozoic cuticles are not petri- 

 fied ; they are only slightly altered, and have retained the power 

 of swelling in water, being able to take up stains like recent 



1 James (93«), translation of a paper by M. Ferry in the Bevue Myeologique, 

 1893. 



2 ZeiUer (82). 



