100 



FOSSIL PLANTS. 



The large Sigillaria, described in the ' Philosophical Transactions,' does not show- 

 many cicatrices of leaves on its outside, and is not of great size as a specimen of that 

 genus, but it is the largest found by me in a calcareous nodule in a seam of coal. It is 

 probable that it may have been portion of a main root, rather than a stem ; for those 

 portions of Sigillaria, whatever the characters of the stem, show nothing but irregular 

 ribs and furrows on their surface. There are generally twenty-four of these main roots 

 to one stem. In structure, however, it agreed with Brongniart's Sigillaria elegans 

 more than any other tlien known plant ; and it was classed with Sigillaria chiefly on 

 that ground. 



Owing to the small size of the nodules in coal, in which the fossil wood is found, we 

 can never expect to find any very large specimens ; for ten inches is the diameter of a 

 very large nodule. Portions of Sigillaria reniformis, S. alternans, S. catenulata, 

 S. tesselata, and S. orgamm have come under my observation, clearly showing the 

 structure of the outer radiating cylinder or inner bark (first noticed in Brongniart's 

 specimen), sometimes reaching to as much as five or six inches in thickness, and 

 enveloped in a stout outer bark, converted into bright coal ; but they are all destitute of 

 the internal radiating cyhnder and the medulla. The absence of the latter is what 

 might have been anticipated, as it is so generally absent in Stigmaria ; but why the 

 former should not be met with is not so evident, except that in large trees, at the present 

 day, decomposition commences in the centre, and extends towards the circumference ; 

 and so it may have been in ancient times. The tannin in the bark may have had greater 

 power to resist decomposition than the inner parts of the tree. 



In my figured specimens of small Sigillaria vascularis, the medulla is in a perfect 

 condition ; but in the large specimens of that plant, and in Biploxglon, described by me 

 in the 'Philosophical Transactions' for 1865, the central portion of the medulla is 

 somewhat disarranged. Since the publication, however, of that Memoir fresh transverse 

 sections of the large specimen of S. vascularis have been made, which prove beyond 

 question that the whole of the medulla is composed of barred tubes. 



In my description of the inner radiating cylinders of the large specimens, mention is 

 made of medullary rays of various breadths, some much narrower than the diameter of 

 the tubes they traverse, and others considerably broader, corresponding with what 

 Professor Williamson has since designated " primary and secondary rays." These are 

 termed medullary rays or bundles^ in the Memoir, and they chiefly relate to the primary 

 rays, but there are also numerous medullary rays of one and two cells in breadth. They 

 were met with in both JDiploxylon and Sigillaria vascularis ; and, although the divisions 

 in the radiating cylinder of the former might appear to indicate that vascular bundles, 



' In my paper I used the term "medullary rays or bundles," owing to the large rays being composed 

 of vascular tubes and not of cellular tissue, as is generally the case in recent plants ; but the smaller ones 

 were of cellular tissue, like ordinary medullary rays. Objection may be made to the term, but in using it 

 no hypothesis is advanced. 



