176 THE CANADIAN NATURALIST. [Yol. vii. 



dullary rnys iu Sigillaria and Stigmaria, contrary to the testimony 

 of Bronguiart, 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 consequence of deca3\ The fact that the me- 

 dullary rays have decayed, leaving the wood 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 fissures in 

 decaying exogenous woods are a consequence of the existence of 

 medullary rays, [or that water-soaked wood canuot be cracked iu 

 this way.] 



Perhaps the grossest of all Mr. Carruthers' histological errors 

 is his affirming that some of my specimens of Prototaxites. show 

 merely cellular structures, or are, as he says, " made up of 

 spherical cells." Now, I affirm that in all my specimens the 

 distinct fibrous structure of Prototaxites occurs, but that in parts 

 of the larger trunks, as is usual with fossil woods, it has been re- 

 placed by concretionary structure, or by that pseudo-cellular 

 structure which proceeds from the formation of granular crystals 

 of silica in the midst of the tissues. Incredible though it may 

 appear, I know it to be a fact, as all the specimens I gave to Mr. 

 Carruthers had been sliced and studied by myself, that it is this 

 crystalline structure which the botanist of the British Museum 

 mistakes for vegetable cells. ^^ I think it right to state here that 

 I not only gave Mr. C. specimens iu these difterent states of pre- 

 servation, but that I explained to him their nature and origin. 



3. Affinities. — In discussing these I must repeat that we must 

 bear in mind with what we have to deal. It is not a modern 

 plant, but a contemporary of that " ]3rotot3^pe of gymnosperms " 

 Aporoxylon, and similar plants of the Devonian. Further, the 

 comparison should be not with exogens in general, or conifers in 

 general, but with Taxineae, and especially with the more ancient 

 types of these. Still further, it must be made with such wood 

 partly altered by water-soakage and decay and fossilized. These 



* In fossil-woods, the carbonaceous matter, being reduced to a 

 pulpy mass, sometimes partly becomes moulded on the surfaces of 

 hexagonal or granular crystals, in such a manner as to deceive very 

 readily an observer not aware of -this circumstance. 



