

stone, retaining their rotundity of fbrm even when prostrate; and 

 are thoroughly penolrutcd with silica except the thin coaly bark. 

 Not only are Algae incapable of occurring in this way, but even 

 the less dense and durable land plants, as Sigillaria3 and Lepi- 

 dodendra are never found thus preserved. Only the extremely 

 durable trunks of coniferous trees are capable of preservation 

 under such circumstances. In the very beds in which these oc- 

 cur, Lcpidodendra , tree ferns and Fs'dopliyton, are flattened into 

 mere coaly films. This absolutely proves, to any one having ex- 

 perience in the mode of occurrence of fossil plants, that here we 

 have to deal with a strong and durable woody plant. 



These considerations were dwelt on in my published descrip. 

 tions of Prototaxites, but they naturally have more weight in my 

 judgment than in that of Mr. Carruthers. Geologists and palae- 

 ontologists will appreciate them. 



2. Microscojnc Structure. — It would be tedious to go into the 

 numerous scarcely relevant points which Mr. Carruthers raises on 

 this subject. I may say in general that his errors arise from 

 neglect to observe that he has to deal not with a recent but a fos- 

 sil wood, that this wood belongs to a time when very generalized 

 and humble types of gymnospcrms existed, and that the afl&nities 

 of the plant are to be sought with Taxincae, and especially with 

 fossil Taxineae, rather than with ordinary pines. 



Mr. C, after describing Prototaxites according to his own 

 views of its structure, expresses the opinion that '* the merest 

 tyro in histological botany " may see that the plant could not be 

 phaenogamous. But if the said tyro will take the trouble to refer 

 to the beautiful memoir on the Devonian of Thuringia, by Richter 

 and Unger,* and to study the figures and descriptions of Apor 

 oxylon primigenium^f Stigmaria annidari8,Calamopterts debilis, 

 and Calamosyrinx Devonicus, he will find that there are Devonian 

 plants referred by those eminent palaeontologists to Gymnosperms 

 aod higher Cryptogams, which fall as far short of Mr. Carruthers' 

 standard as Prototaxites itself Nothing can be more fallacious 

 in fossil botany than comparisons which overlook the structures 

 of those primitive palaeozoic trees which in so many interesting 

 Ways connect our modern gymnosperms with the cryptogams. 



•■Trans., Vienna Academy, 1856. 



t I have elsewhere compared Aporoxylon with Prototaxites, ' Jour, 

 Oeol. Soc' 1862, p. 306. Report on Devonian plants. 



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