CARBONIFEROUS LYCOPODS AND SPHENOPHYLLS. 103 



from the presence of an exogenous zone, Sigillaria was supposed 

 to represent a phanerogamous type of plant structure. It is now 

 well known, however, that the presence of an exogenous zone is 

 characteristic of palaeozoic cryptogams.' 



For manj' years nothing was added to the knowledge of the 

 internal structure of Sigillaria until Renault and Grand 'Eury 

 described the structure of a specimen they identified as Sigillaria 

 spinulosa.- This specimen shows the same type of vascular 

 structure as that originally described by Brongniart, and it was 

 supposed that the separate bundles, composed of primary and 

 secondary xylem, which formed the hollow vascular cylinder, 

 gave to Sigillaria a type of structure peculiar to itself and quite 

 distinct from that of Lepidodendron, where both the primary and 

 secondary xylem formed a closed ring — that is, that in Lepido- 

 dendron the vascular system did not consist of a number of 

 separate bundles, but of a ribbon-like band. This distinction 

 does not really exist, for the so-called Sigillaria type passes 

 insensibly into the Lepidodendron type. Solms-Laubach has 

 pointed out in the specimen of Sigillaria spinulosa which he 

 figures in his Fossil Botany that some of the primary vascular 

 bundles are clearly united laterally,^ and in a specimen of the 

 same species, which was most kindly given to me by jNIonsieur 

 Renault, the lateral union of the primary bundles is more com- 

 plete.^ In this example there is, in part at least, the occurrence 

 of the closed primary bundle of Lepidodendron. 



There is also in the British Museum a specimen of a 

 Rhytidolepis-Sigillaria, with the internal structure preserved, 

 still awaiting description, but which, according to the statement 

 of Williamson and Hartog, " has the continuous cylinder and all 

 the internal organization of Corda's Diploxylon."^ I had also 



* A secondary development of tissue occurs in the bundle of Isoetes. 

 See A. de Bary, Comparative Anatomy of the Vege'.ative Organs of the 

 Phanerogams and Ferns, English Ed., p. 623. 1884. 



' " Recherches sur les vegetaux silicifies d'Autun : Etude du Sigillaria 

 spinulosa." Mem. presentes par divers savants a I'Acad. d. Sciences, 

 Vol. XXII. 1875. Paris. 



3 Foiisil Botany, English Ed., p. 253, fig. 29. 1891. 



* KiJston, Trans. Roy. Soc. Edin., Vol. XXXIX., Part i., Xo. 5, p. 41, 

 figs. A, B, C. 1897. 



^ See Solms-Laubach, Fossil Botany, p. 254. 



