1869.] CAREFTHERS SIGILLARIA. 251 



The absence, then, of any true medullary ray excludes the Stig- 

 maria from the Dicotyledons, and places it beyond doubt among the 

 Cryptogams ; and this is further confirmed by the fact that the 

 whole of the vascular tissue is composed of scalariform vessels, which 

 are not known to make up the whole of the vascular tissue of any 

 plants except among the Crjptogamia. 



As the internal structure of the root is the same as that of the 

 stem, we ought to find in the latter an absence of true medullary rays, 

 and the existence only of a vascular horizontal system communicating 

 with the axial appendages. 



Brongniart's elaborate memoir on Sigillaria elegans still supplies 

 the most detailed account of the internal structure of the stem of 

 this genus. It consists of a central cellular axis, or medulla, sur- 

 rounded by a vascular cylinder ; and this, again, is invested by a thick 

 cellular cortical layer, the outer portion of which is composed of 

 fusiform cells of less diameter than those of the inner portion. So 

 far this is precisely what is found ia Stigmaria ; but the vascular 

 cylinder is, according to Brongniart, broken up by numerous delicate 

 medullary rays, whose tissue, however, is destroyed. He was unable 

 to detect the least trace of the cells ; yet he assumes without any hesi- 

 tation or doubt that the openings between the radiating lines of the 

 vascular tissue are certain indications of medullary rays, and points 

 out that the difference between Lepidodendron Harcourtii, which 

 Lindley and Hutton had described, and his own Sigillaria elegans 

 lay entirely in the possession of medullary rays by his plant. "When, 

 however, the figures of Brongniart are compared with the numerous 

 specimens which have been discovered since, many of which have 

 been figured, and especially with those published by Binney under 

 the name of Sigillaria vascvkiris (which, however, are species of 

 Lepidodendron) , it is easy to see that he wrongly interpreted the 

 series of cracks in the small fragment he was examining, just as I 

 have shown he did in Bobert Brown's specimen of Stigmana. The 

 beautiful longitudinal section cut parallel to the supposed medullary 

 rays (pi. iii. fig. 2) is without any trace of the muriform structure ; 

 and it ought to have been seen here if it ever existed. The sup- 

 posed ends of the medullary rays shown in fig. 203 of plate iv. are 

 much more like the results of desiccation or decay than the sections 

 of rays ; and the aspect of the adjoining scalariform vessels does not 

 agree with what would have been produced by a medullary ray upon 

 the vascular tissue forming the margins of the mesh through which 

 it passes. 



Brongniart's interpretation of these spaces is repeated by him in 

 his ' Tableau, ' and is adopted by all subsequent writers. It forms 

 the real difficulty in the way of Dr. Hooker's referring without hesi- 

 tation the genus to Lycopodiaceoe. 



In Dr. Dawson's valuable contribution to our knowledge of the 

 Coal-flora, he describes the medullary rays as existing in Sigillaria, 

 in addition to the vascular bundles belonging to the axial appendages ; 

 but neither in his letterpress nor his plates can I determine whe- 

 ther this arises from the already adopted diagnosis of the genus, or 



VOL. XXV. PART I. T 



