436 



STRUCTURE OF STIGMARIA. 



series concentric with but exterior to the wood, then will the arrange- 

 ment coincide with that of Lepidodendron in these important points, and 

 the Sigillaria in question may be pronounced a Lepidodendron with the 

 vascular system broken up into wedges divided by medullary rays, and 

 further possessed of a third system of vessels placed in juxta-position to 

 and within that of the wood. 



The accompanying wood-cuts explain these arrangements of the 

 tissues in Stigmaria (a.), Lepidodendron (b.), and Sigillaria (c), the 

 latter both according to M. Brongniart's view, and in the light wherein 

 I regard it. In all, the letter a indicates the vascular tissue of the 

 wood ; b, that from which the leaves are supplied ; and c indicates the 

 third series in Sigillaria. 



Fig. 1. 



A. 



B. 



I| b 



k \l 



Under any circumstances, the most complex of these plants is the 

 Sigillaria, in which the vascular tissue surrounding the axis is as 

 independent of the foliage and as free, as are the similar vessels in 

 Lycopodium, which also pass down the pith within the wood, and send 

 off no bundles to the leaves. 



