medullary rays, [or that water-soaked wood caiiDOt be cracked in 

 this way.] 



Perhaps the grossest of all Mr. Carruthers' histological errors 

 is his affirming that Kiuie of my specimens of Prototaxites show 

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

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

 distinct fibrous structure of Prototaxites occurs, but tluitin 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 fr(»m the Ibrmation 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 in these different states of pre- 

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



It is unnecessary to follow further the histological part of the 

 question, as my object is not so much to expose the errors of Mr. 

 Carruthers as to illustrate the true structure of Prototaxites. 



3. Ajfuilties. — 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 "prototype 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 Taxineau, and especially with the more ancient 

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

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

 necessary preliminaries to the question appear to have been alto- 

 gether overlooked by Mr. Carruthers. 



3Iy original determination of the probable affinities of Proto- 

 taxites, as a very elementary type of taxine tree, was based on 

 the habit of growth of the plant — its fibrous structure, its spirally- 

 lined fibres, its medullary rays, its rings of growth, and its coaly 

 bark, along with the durable character of its wood, and its 

 mode of occurrence ; and I made reference for comparison to 

 other Devonian woods and to fossil taxine-trees. 



" In fossil-woods, the carbonaceous matter, licing ncKiccd to a 

 puipy mass, Rometimes partly becomes raouklcd on the surfaces of 

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

 re idily an observer not aware of this circumstance. 



