26 BIOLOGICAL LECTURES. 



various cavities are filled with the calcite, silica, or other 

 infiltrated material.^ 



Plants from the early Palaeozoic are often most beautifully- 

 preserved in this way, but cases occur in which the recrystalli- 

 zation of the infiltrated material brings about a redistribution 

 of the carbon particles in such a way as to produce a false 

 structure, as found most notably in the Celluloxylon primaevum 

 of Dawson, which was originally supposed to represent a purely 

 cellular plant, the component cells of which were of gigantic 

 size. More recent studies of this material, and comparison 

 with other well-determined plants in various conditions of 

 alteration and petrifaction, have afforded ample proof that the 

 apparent structure of Celluloxylon is nothing more nor less than 

 a condition incident to petrifaction, in which the carbon of the 

 original structure has been redistributed through the influence 

 of crystallization and deposited upon the surfaces of, or other- 

 wise between, the adjacent crystals. 



Two full centuries have passed since the first observations 

 upon the occurrence of fossil plants were made. Yet palaeo- 

 botany has only recently attained to a position commensurate 

 with its importance as a branch of botanical science from which 

 most important and necessary data respecting the gradual evo- 

 lution of the higher plants may be gained. During the seven- 

 teenth century, when men were still experiencing the^ influence 

 of the Middle Ages, the discovery of plant and animal remains 

 in the crust of the earth was well calculated to call forth in all 

 seriousness the most remarkable explanations of their occur- 

 rence. And among other things we are thus told that such 

 evidence gave proof " that the whole terrestrial globe was 

 taken all to pieces and dissolved at the Deluge, the particles 



^ A most instructive example of the extent to which a given material may be 

 involved in the process of petrifaction is afforded by Osmundites skidegatensis 

 Penh, from the Cretaceous of Vancouver Island. An analysis shows it to contain 



Calcite 70.46% 



Silica 12.15% 



Combustible matter .... 17.36% 



IGC.00% 



The last constituent which disappears upon ignition, leaving a calcined mass, 

 probably represents the amount of carbon residue derived from the original plant. 



