192 TRANSACTIONS AND PROCEEDINGS OF THE [Sess. lxiii. 



polished cross section, one notices particularly a marginal 

 band, creamy white in colour, and of variable breadth from 

 2 to 5 mm., passing right round the stem. The remainder 

 and larger part of the section enclosed by this is of a 

 mottled dark colour, in fact, by a fortunate coincidence, 

 « the tint of a photomicrograph fairly well corresponds to 

 that of the actual specimen. While the minute structure 

 is on the whole very well preserved throughout, it is most 

 exquisitely so in the white peripheral zone. It is doubtful 

 whether this difference in colour, accompanied as it is 

 by a difference in the degree of perfection of preservation 

 of the anatomical structure, is to be ascribed to peculi- 

 arities of silicification, or represents some ])riniary differ- 

 entiation in the original wood itself into alburnum and 

 duramen. I am inclined to believe that the latter is the 

 explanation. 



With the naked eye, one can discriminate the annual 

 rings, sharply limited by a thin white line ; medullary 

 rays, as delicate sinuous threads on the darker matrix, of 

 marked continuity ; tracheae, as small dark spots of uniform 

 distribution. 



Viewed microscopicall}^ the wood appears to have been 

 composed of a ground mass of fibres, quadrangular in 

 section, and arranged in very regular radial rows ; among 

 these are embedded trachea, equable in size, not very 

 abundant, but uniformly distributed. The fibres average 

 0'01875 mm. in diameter, while the pores measure 

 0*1071 mm. in tangential and 0'1285 mm. in radial 

 diameter. The pores occur singly, or often in radial 

 groups of two to six or more. 



The medullary rays are numerous, about 60 per 5 

 millimetres ; they are of two sizes, and are not very 

 uniformly distributed. Their breadth varies from "0107 

 to '0375 mm.; the larger ones have great persistence, and 

 can be traced from pith out to the periphery. 



The annual rings appear distinctly marked by a narrow 

 white line without pores ; they indicate a very slow 

 growth, giving about 32 rings per inch of radius. The 

 wood in this and other respects, such as character of the 

 rays, recalls that of some Euphorbiaceous trees, Buxus 

 among others. It also resembles, in some respects, recent 



