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THE GEOLOGICAL HISTORY OF PLANTS. 



occupied witli pyrites, obscurely represent the medullary rays, which 

 must have l»cen very feebly developed. 'J'ho radiating bundles 

 passing to the leaves run nearly horizontally ; but their structure 

 is very imrcrfecttly jjreserved. 'J'ho stem Ijeing old and probably 

 long deprived of its leaves, they may have been partially disorganised 

 before, it was fossilised. TIk; outer surface of th(! axis is slriaU'd 

 longitudiiuilly, and in some places marked with imfircssions of tort- 

 uous libres, apf)ar(!ntly those of the inner bark, in the cross-sec- 

 tion, where weathered, it shows concentric rings; but under the 

 mi(!roscop(! thes(! ai)p<'ar rather as bands of compressed tissue than 

 as proper lines of growth. They are alxjut twenty in iiumlM'r. This 

 tree has an erect, ribbed trunk, twelve feet in height and fifteen 

 inches in diameter, swc^lling to about two feet at the base. 



2. Fdi'iilurid 'J'ypc. — This has been well described by Urongniart 

 and by Renault,* and dilTers from the above chiefly in the; fact that 

 the outer exogenous woody zoiu; is comi)os('d of reticulatc.'d instead 

 of scalariform li-.iue, and the inner /one is of the peculiar form 

 which 1 have (iharacterised as pseudo-scalariform. 



8. Siyillaria l*ropcr. — This I have, illustrated in my paper in 

 the "Journal of the Geological Society" for May, 1H71, and it ap- 

 peal's to repnist^nt the highest and most perfect type of the larger 

 riblied Sujillarin. 1'his structure; I have; (les(;ribed as follows, bas- 

 ing my descrij)t ion on a very lim; axis found in an erect stem, and 

 on the fragments of the woody axis found in the bases of other erect 

 stems : 



a. A dense ct ''...lar outer bark, usually in the slate of compact 

 coal — but wh( II its structure is preserved, showing a tiH.sue of thick- 

 ened parenchymatous cells. • 



h. A very thick inner bark, which has iismilly in great part 

 perished, or been converted into (!oal, but which, in old trunks, con- 

 tained a large; <|uantity of prosenehymatous tissue, very tough and 

 of great durability. This "bast-tissue" is comparable with that of 

 the inner bark of modern conifers, and constitutes much of tiie min- 

 eral charcoal of the coal-seams, 



c. An outer ligneous cylinder, composed of wood-cells, (lither 

 with a single row of larg(! bordered [)ores,f in the numtier of pines 



* "Uotani(pie Fossile," Paris, 1881. 



f These are the same with the wood-cells elsewhere called diHcigorouB 

 tissue, and to which I have applied the terms unipoious and multiporoua. 

 The markings on the walls are caused by an unlincd p ,.tion of the cell- 

 wall placed in a disk or depression, and this often surrounded by an 



