﻿BIBLIOGRAPHY. 



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shown in pi. xxxi of the natural size, but here magnified 5 diameters, exhibiting the 

 central axis composed of hexagonal vessels arranged without order, of several sizes, those 

 in the middle being smaller, and becoming larger towards the outside, where they come 

 in contact with the internal radiating cylinder, b, and then again diminishing in size. 

 This latter was no doubt cylindrical, like the stem of the plant ; but both parts in the 

 process of petrification have been altered by pressure to their present forms. It consists 

 of a broad cylinder, b, about an inch in diameter, composed of parallel elongated tetra- 

 gonal or hexagonal tubes, of equal diameter throughout for the greater part of their 

 length, obtuse and rounded at either extremity, and everywhere marked with crowded 

 parallel lines, which are free or anastomosing all over the surface. The tubes towards 

 the axis are of the smallest diameter ; they gradually enlarge towards the circumference, 

 where the largest are situated, though bundles of smaller tubes occasionally occur among 

 the larger. This cylinder, which, for convenience, may be called the internal woody 

 system of the plant, is divided into elongated wedge-shaped masses, pointed at their 

 posterior or inner extremity, and parted by fine medullary rays, of various breadths, 

 some much narrower than the diameter of the tubes, others considerably broader ; but 

 none are conspicuous to the naked eye, except towards the outer circumference in some 

 rare instances. 



" Pig. 2 represents a transverse section of the central axis and the commencement of 

 the internal radiating cylinder, magnified 12 diameters. The hexagonal vessels in 

 the centre and at the circumference, where thev come in contact with the internal 

 radiating cylinder, are smaller in size than those seen in the other parts of the axis. 

 The dark line across the axis, as well as the dark space in the centre, 'both seem to be the 

 result of a disarrangement of the tubes during the process of mineralization, as similar 

 appearances have not been observed in many other specimens examined by me, which in 

 those parts are in a more perfect state of preservation. The dark and sharp line 

 separating the vessels of the central axis from those of the internal radiating cylinder 

 does not permit us to clearly see the origin of the medullary rays or bundles which 

 undoubtedly traverse the latter. 



" Pig. 3 represents a longitudinal section taken on the right-hand side of the 

 specimen, and extending across the whole of the internal radiating cylinder, through the 

 central axis, the intermediate space between the internal radiating cylinder and the outer 

 cylinder, and the external radiating cylinder, to the outside of the stem, magnified 4 

 diameters ; a, a showing the smaller barred vessels of the central axis, having some {a, a) 

 which appear to have been disarranged ; b, b the internal radiating cylinder of larger 

 barred vessels ; c the space occupied by lax cellular tissue, traversed by bundles of vessels ; 

 and d the external radiating cylinder, consisting of elongated tubes, or utricles, arranged 

 in radiating series, diverging from certain circular openings, and divided by masses of 

 muriform tissue, which contain the medullary rays or bundles. 



" Pig. 4 is a tangential section of the same parts of the specimen as lastly described, 



