Hick : On the Fossil Plants of the Coal Measures. 101 



volcaDic ash^ but in a few instances by vegetable (debris introduced 

 from without ; and in one specimen, imbedded in the vegetable mass, 

 are several diploxyloid axes, of very old stems." By some authorities 

 these axes have been regarded as young growths that sprang up within 

 the cylinders of bark after the inner tissues of the stems had been 

 destroyed ; but Prof. Williamson is of opinion that this is an error, 

 their magnitude and decorticated condition, as well as the nature of 

 the materials with which they are intermixed, pointing rather to the 

 conclusion that they have been introduced from without. A question 

 of primary importance was the botanical character of these stems, as 

 indicated by the remains of their bark, and by the nature of the 

 numerous fragments of twigs, branches and fruits in the overlying 

 beds ; and the course of the investigations which Prof. Williamson 

 undertook was shaped with a view to its solution. The results, which 

 are here given with the most ample details, show unmistakably that 

 the stems in question are all lepidodendroid in nature, and that they 

 present none of the characters that should be met with had their 

 affinities been rather with the Sigillar'nB. It is true that the surface 

 is marked longitudinally by a number of fissures which at first sight 

 suggest a comparison with those of Sigillaricd, but on closer examina- 

 tion they are found to be of mechanical rather than of organic origin, 

 while, as we have said, the characteristic structure of Sigillarics is 

 altogether absent. On the other hand, the composition and arrange- 

 ment of the tissues of the stems, so far as they are preserved : the 

 structure of the leaves ; and the form and arrangement of the leaf- 

 scars, are all of the lepidodendroid kind, so that there is both negative 

 and positive evidence of the strongest kind in support of the con- 

 clusion arrived at. 



The general nature of the specimens being thus determined, the author 

 proceeds to a detailed description of their structure as exhibited in 

 thin sections prepared for microscopical examination. The description 

 is drawn up in excellent style, and is accompanied by well-executed 

 illustrative figures, as in the previous memoirs. Both the descriptions 

 and the figures bear out the interpretations put upon the specimens in 

 the previous paragraphs, and incidentally throw light on the somewhat 

 vexed question, the affinities of the Sigillari/je. As is well known to 

 those who keep themselves an coitrant with these investigations, 

 MM.' Brongniart and Renault, the eminent French pahTo-botanists, 

 are of opinion that while the Lepidodendra are undoubtedly crypto- 

 gams closely allied to existing Lycopods, the Sigillarice belong to 

 higher order of vegetable life, and are to be ranked as exogenous 



