STRUCTURE OF STIGMARIA 435 



* 



portion of the Sigillaria? figured by M. Brongniart, and in other fossils 

 contained in the Museum of the Survey, and is probably owing to their 

 great delicacy, for they are much more membranous in appearance than 

 the similarly marked vessels of the wood. 



The most important circumstance thus developed is the existence 

 of a double system of vessels in Stigmaria, first shown by Goeppert, 

 and the consequent approach in this respect to Diploxylon* Corda. 

 In Diploxylon, however, the inner system forms a continuous cylinder, 

 concentric with and in juxta-position to the wedges of wood forming the 

 outer ; whilst in Stigmaria the same inner system is broken up into 

 scattered bundles apparently unsymmetrically arranged in the medullary 

 axis or pith of the plant. 



In Lepidodendron again there is the same double vascular system ; 

 but that, from which the bundles arise which proceed to the leaves, is 

 placed externally to the wood, where it forms a continuous zone with a 

 well-defined inner edge (in juxta-position with the outer circumference 

 of the inner zone) and a sinuous outer edge, from which the diverging 

 bundles are given off. Such is also the arrangement in the axis of 

 Lepidostrobus. 



Sigillaria elegans differs from all the above. The woody system is 

 (as in Stigmaria) broken up into wedge-shaped plates, separated by 

 medullary rays ; and another vascular system (from which, possibly, the 

 leaves are supplied) forms f a series of bundles in the medullary axis of 

 the stem, each placed opposite the wedges of wood. The bundles 

 which immediately supply the leaves again are also placed opposite the 

 wedges of wood, but externally to them, in this respect differing from 

 Stigmaria, where they are opposite the medullary rays, and from Lepi- 

 dodendron, where they form a continuous zone. It is, however, doubtful 

 to M. Brongniart whether in his Sigillaria? the system of vessels wliich 

 supplies the leaves really communicates with that immediately sur- 

 rounding the pith. To me that structure appears improbable, from the 

 position of both being alternate with the medullary rays through which 

 the vessels should pass. This then is a very important point to clear 

 up ; for if the inner and outer bundles of tissue in Sigillaria? communi- 

 cate through the medullary rays, then will the arrangement be nearly 

 identical with that of Stigmaria. If, according to Brongniart's views, 

 on the other hand, the outer bundles from which the leaves are supplied 

 have no communication with the innermost, and form an independent 



* Corda, Flora der Vorwelt, p. 34, tab. xi. 



f On this point M. Brongniart is not satisfied, not having seen the bundles which 

 traverse the cutical portion in the medullary rays, which might be expected if they com- 

 municated with the system of vessels within the wood and immediately surrounding the 

 pith. 



II. 2 H 



