.":no. 2.] 



NOTES ON PROTOTAXITES. 



177 



^necessary preliminaries to the question appear to have been alto- 

 ,?gether overlooked by Mr. Carruthers. 



My original determination of the probable affinities of Proto- 

 '"laxites, 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 

 ■'iDark, along with the durable character of its wood, and its 

 ;inode of occurrence ; and I made reference for comparison to 

 ^•other Devonian woods and to fossil taxine-trees. 



Mr. Carruthers prefers to compare the plant as to structure 

 -with certain chlorospermous Algse, and as to size with certain 

 gigantic Melanosperms, not pretended to show similar structure. 

 This is obviously a not very scientific way of establishing affini- 

 •ties. But let us take his grounds separately. He selects the 

 ■little jointed calcareous sea-weed Halimeda ojnmtia, as an 

 allied structure, and copies from Kutzing a scarcely accurate 

 figure of the tissue of the plant as seen after the removal of its 

 calcareous matter.^ He further gives a defective description of 

 .this structure; whether taken from his own observation or from 

 Kutzing, he does not say. Harvey's description, which I verified 

 several years ago, in an extensive series of examinations of these cal- 

 :careous iilgae, undertaken in cousequenceof a suggestion that Eo- 

 zoon mio;ht have been an oro-anism of this nature, is as follows: — 

 ■ °' x\fter the calcareous matter of the frond has been removed by acid 

 a spongy vegetable structure remains made up of a plexus of slender 

 longitudinal unicellular filaments constricted at intervals, and at 

 the constrictions emitting a pair of opposite decompound, dicho- 

 ". tomous, corymboso-fastigiate horizontal ramelli, whose apices co- 

 here and form a thin epidermal or peripheric stratum of cells." 

 It will be seen at once that this structure has no resemblance 

 whatever to anything existing in Prototaxites, even as interpreted 

 "by Mr. G., and without taking into account the fact that Hali- 

 meda opuntia is a small calcareous sea-weed, divided into flat 

 : reniform articulations, to which this structure is obviously suited, 

 .as it would be equally obviously unsuited to the requirements of 

 .-a thick cylindrical trunk, not coated with calcareous matter. 



In point of size, on the other hand, Mr. Carruthers adduces 

 •Jiihe great Lessonia of the Anta rctic seas, whose structure, how- 



* A more characteristk: i 

 '.can Algie." 



Wox. Til. 



L- 



veil in Harvej-'s " North Ameri- 



No. 3. 



