GEOLOGY AND NATURAL HISTORY. 477 



process of condensation has been carried much farther than in that described by 

 Professor Williamson, in which a portion of the unaltered pith remained between 

 the Sternbergia-cast and the wood. It thus more fully explains the possibility of 

 the preservation of such hollow chambered piths, after the disappearance of the 

 wood. It also shows that the coaly coating investing such detached pith casts is 

 not the medullary sheath, properly so called, but the outer part of the condensed 

 pith itself. 



The examination of this specimen having convinced me that the structure of 

 Sternbergia} implies something more than the transverse cracking observed in 

 Juglandaceas, I proceeded to compare it with other piths, and especially with that 

 of Cecropia Peltata, a West Indian tree, of the natural family Artocarpaceae. 

 This recent stem is two inches in diameter. Its medullary cylinder is three-quar- 

 ters of an inch in diameter, and is lined throughout by a coating of dense whitish 

 pith tissue, one-twentieth of an inch in thickness. This condensed pith is of a 

 firm corky texture, and forms a sort of internal bark lining the medullary cavity. 

 Within this the stem is hollow, but is crossed by arched partitions, convex upward. 

 These partitions are of the same white corky tissue with the pith lining the cavity, 

 and on their surfaces, as well as on that of the latter, are small patches of brown- 

 ish large-celled pith, being the remains of that which has disappeared from the 

 intervening spaces. 



Inferring from these appearances that this plant contains two distinct kinds of 

 pith tissue, differing in duration and probably in function, I obtained, for compari- 

 son, specimens of living plants of this and allied families. In some of these, and 

 especially in a " Ficus Imperialis," from Jamaica, I found the same structure ; and 

 in the young branches, before the central part of the pith was broken up, it was 

 evident that the tissue was of two distinct kinds — one forming the outer coating 

 and transverse partitions opposite the insertions of the leaves, and retaining its 

 vitality for several years at least ; the other occupying the intervening spaces or 

 intemodes, of looser texture, speedily drying up, and ultimately disappearing. 



Another variety of the Sternbergia-like pith structure appears in a rapidly 

 growing exogenous tree with opposite leaves, cultivated here, and I believe a 

 species of Paullinia. In this trunk there are thick nodal partitions, and the inter- 

 vening spaces are hollow and lined with firm corky pith, with its superficial portion 

 condensed into a sort of epidermis, and marked with transverse wrinkles ; a cast 

 of which would resemble those Sternbergias which have merely wrinkles without 

 diaphragms. 



The trunks above noticed are of rapid growth, and have large leaves ; and it is 

 probable that the more permanent pith tissue of the medullary lining and parti- 

 tions serve to equalize the distribution of the juices of the stem, which might 

 otherwise be endangered by the tearing of the ordinary pith in the rapid elonga- 

 tion of the internodes. A similar structure has evidently existed in the coal for- 

 mation conifers of the genus Dadoxylon, and possibly they also were of rapid 

 growth, and furnished with very large or abundant leaves. 



Applying the facts above stated to the different varieties or species of sternbergia, 

 we must in the first place connect with these fossils such plants as the Pinites 

 Medullaris of Witham. All are distinctly coniferous, and the differences that ap- 

 pear may be due merely to age, or more or less rapid growth. 



Other specimens of sternbergia want the internal partitions, which may, how- 

 ever, have been removed by decay ; and these often retain very imperfect traces, 



