428 THE CARBONIFEROUS SYSTEM. 



triangular leaf-scars, arranged in quincuncial order on the surface of 

 the stem. 



Inferring from these appearances that this plant contains two distinct 

 kinds of pith tissue, differing in duration and probably in function, I 

 obtained, for comparison, specimens of living plants of this and allied 

 families. In some of these, and especially in a species labelled " Ficus 

 i7nperial{s," 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. 



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 partitions serves 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 elongation of the internodes. A similar 

 structure has evidently existed in the Coal formation 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 Sternbei'gia, we must, in the first place, connect with these fossils 

 such plants as the Pinites medullaris of Witham. I have not seen a 

 longitudinal section of this fossil, but should expect it to present a 

 transverse structure of the Sternbergia type. The first specimen de- 

 scribed by Professor Williamson represents a second variety, in which 

 the transverse structure is developed in the central part of the pith, 

 but not at the sides. In my Pictou specimen the pith has wholly dis- 

 appeared, with the exception of the denser outer coating and transverse 

 plates. All these are distinctly coniferous, and the differences that 

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



Other specimens of Sternbergia want the internal partitions, which 

 may, however, have been removed by decay ; and these often retain 

 very imperfect traces, or none, of the investing wood. In the case of 

 those which retain any portion of the wood sufficient to render prob- 

 able their coniferous character, the surface markings are similar in 

 character to those of my Pictou specimen, but often vary greatly in 

 their dimensions, some having fine transverse wrinkles, others having 

 these wide and coarse. Of those specimens which retain no wood, 

 but only a thin coaly investment representing the outer pith, many 

 cannot be distinguished by their superficial markings from those that 



