STIGMARIA. 273 



lining the wall of the hollow cylinder. Similar remains of parenchyma are 

 also figured by Goppert *, but these are according to his account traversed 

 by isolated tracheal strands, which emerge further on through the primary 

 rays and give rise to the traces of the appendages. Though it is not easy 

 to reconcile this statement with Brongniart's 2 fine figure, yet it has been 

 adopted by Hooker 3 and by Binney 4 . That Binney has been deceived in 

 this matter is evident from a glance at his figure. His tracheal strands are 

 only transverse sections of appendages of Stigmaria, which, as so very fre- 

 quently happens, have found their way through exuberance of growth into 

 the interior of the specimen. Williamson, who has pointed emphatically to 

 this source of error 5 , has already suggested that this same mistake may be 

 at the bottom of Goppert's statements ; and by fresh examination of the 

 original specimen, which the kindness of F. Romer placed at my disposal, 

 I have in fact satisfied myself that his view is correct. These statements 

 therefore, on which Renault has relied so much for his conclusions, are not 

 to be trusted. 



It appears however that this central tissue was not composed of pa- 

 renchyma in all Stigmariae, for Renault has found that in his Stigmaria 

 augustodunensis the whole of the space inclosed by the wood was filled 

 with a closed strand consisting of narrow tracheides. He has kindly shown 

 me his preparations, which are all made from the same specimen, the only 

 one which has the central strand preserved. Unfortunately we have received 

 no account of the character of the surface, so that there is still room for 

 doubt whether the specimen belongs to Stigmaria. 



The structure here described enables us to understand certain forms of 

 preservation in the cast, which are noticed in the literature. Williamson 6 

 gives the transverse sections of an inclosed cast, in which the inner cast is 

 separated from the outer by a broad annular interval, and is connected with 

 it only by thin rods of stone which cross the gap like spdkes in a wheel. It 

 is evident that in this case the two casts were formed at the same time. 

 And the ring of wood was also in existence at that time ; the mineral 

 matter could only make its way into the primary rays, in which the tissue 

 had disappeared, and take casts of them. The subsequent disappearance 

 of the wood resulted in the formation of the empty space which is crossed by 

 the isolated rods, the casts of the primary rays. Von Rohl 7 had previously 

 published a similar specimen, and interpreted it quite rightly; but his in- 

 terior cast is broken away, and only the outer portions of the rods which 

 represent the rays are preserved in situ. 



The rind (Fig. 32) which remains to be described, is, as was said above, 



1 Goppert (1), t. 13, f. 31. 2 Brongniart (7), t. 29. 3 Hooker (4). 4 Binney (4), f. 2. 



5 Williamson (1), n, p. 214. 6 Williamson (6), t. 13. 7 von Rohl (1), t. 24. 



T 



