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TUE GEOLOGICAL HISTORY OF PLANTS. 



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ceolate, sessile, entire, with rounded apices and of leathery con- 

 sistency. The leaves urc from twenty to ninety centimetres in 

 length. The nerves are either equally or unequally strong. 



2. Dorycordaites. — Leaves lanceolate, with sharp points ; nerves 

 numerous, fine, and equal in strength. The leaves attain a length 

 of from forty to fifty centimetres. 



3. Poacordaites. — Leaves narrow, linear, entire, lilunt at the 

 point, with nerves nearly equally strong. The leaves are as much 

 as forty centimetres in length. 



To these Renault and Zeiller have added a fourth group, Scuto- 



cordaites. 



Oeyius Sternbeegia. 



This is merely a provisional genus intended to receive casts of 

 the pith cylinders of various fossil trees. Their special peculiarity 

 is *^hat, as in the modern Cccropia peltata, and some species of Ficus, 

 * • pith consists of transverse dense partitions which, on the elonga- 

 tion of the internodes, become separated from each other, so as to 

 produce a chambered pith cavity, the cast of which shows transverse 

 furrows. The young twigs of the modern Abies hahamifera pre- 

 sent a similar structure on a minute scale. I have ascertained and 

 described such pith-cylinders in large stems of Dadoxylon Oxiangon- 

 dianum, and D. materiarium. They occur also in the stems of 

 Cordaites and probably of Sigillarim. I have discussed these curi- 

 ous fossils at length in " Acadian Geology " and in the " Journal of 

 the Geological Society of London," 1860. The following summary 

 is from the last-mentioned paper : j 



a. As Prof. Williamson and the writer have shown, many of 

 the Sternhergia piths belong to coniferous trees of the genus Da- 

 doxylon. 



b. A few specimens present multiporons tissue, of the type of 

 Didyoxylon, a plant of unknown afiinities, and which, according to 

 Williamson, has a Sternbergia pith. 



c. Other examples show a true sealariform tissue, comparable 

 with that of Lepidodendron or Sigillaria, but of finer texture. Corda 

 has shown that plants of the type of the former genus (his Loma- 

 tophloios) had Ster7ibergia piths. Some plants of this group are by 

 external characters loosely reckoned by botanists as ribless Sigillarm 

 {Clathraria)', but I believe that they are not related even ordinal ly 

 to that genus. ' 



d. Many Carboniferous Stemhergim show structures identical 

 with those described above as occurring in Cordaites, and also in 

 some of the trees ordinarily reckoned as Sigillarim. 



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