134 THALLOPHYTA. [CH. 



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 Eenault^ 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 "S/i to 1/x 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" 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. 



In addition to the Micrococcus described by Renault from 

 the Toula paper-coal, there are a host of other forms which 



' Renault (<ih\ (96i) p. 478, (96") p. 106. (Several figures of the cuticles are 

 given in these publications.) 

 ' Eenault (96^) p. 492. 



