often entirely destroyed, and only the ligneous lining remains, 

 perhapsi thickened by iticrustation of mineral matter within. In 

 this case the original lining of the cell may seem to be an exter- 

 nal structure. 1 have examples both in Mesozoic conifers and in 

 carboniferous plants. Long soaking in water and decay have 

 thus often made what miy have been a lining of wood-cells appear 

 as an intercellular matter, or an external thickening of the walls. 

 (3.) In decayed woods the mycelium ol' fungi often wanders 

 through the tif^sues in a matuier very perplexing; and I suspect, 

 though I cannot be certain of this, that some fossil woods have 

 been disorganized in this way. At the time when my descrip- 

 tion was published, I felt uncertain to which of these causes to 

 attribute the peculiar appearance of Prototaxites. I have now, 

 from >«ub.Ne<jueiit study of the cretaceous Taxineoc of British 

 Columbia, ■-!= little hesitation in adopting the first and second ex- 

 planations, or one of them, as probable. 



Mr. Carruthers does not believe in the medullary rays of Proto- 

 taxites. The evidence of these is the occurrence of regular lenti- 

 cular spaces in the tangential section, which appear as radiating 

 lines in the transverse section. The tissues have perished ; but 

 some tissues must have occupied these spaces; and in fossil woods 

 the medullary rays have often been removed by decay, as one 

 sometimes sees to be the case with modern woods in a partially 

 decayed state. Mr. Carruthers should have been more cautious 

 in this matter, after his rash denial, on similar grounds, of me- 

 dullary rays in Sigillaria and Stigmaria, contrary to the testimony 

 of Brongniart, Goeppert, and the writer, and the recent exposure 

 of his error by Professor Williamson. That the wood-cells have 

 been in part crushed into the spaces left by the medullary rays 

 is only a natural conse(iucnce of decay. The fact that the me- 

 dullary rays have decayed, leaving the "vood so well preserved, 

 is a strong evidence for the^durability of the latter. The approval 

 with which Mr. C. quotes from Mr, Archer, of Dublin, the naive 

 statement that " the appearance of medullary rays was probably 

 produced by accidental cracks or fissures," would almost seem to 

 imply that neither gentlemen is aware that radiating fis.sures in 

 decaying exogenous woods are a consequence of the existence of 



• lleport of Geol. Survey of Canada, now in course of publication. 

 The collections contain wood showing the structure of yew, cypress, 

 oak, bfrch, and poplar, all from rocks of cretaceous age. 



