S1GILLARIEAE. 255 



most cortical layer composed of stout parenchyma, the elements of which 

 are directed inwards in rows ; it is therefore of small importance. What 

 Dawson * has termed Sigillaria-structure is so imperfectly described by him 

 that we can arrive at no conclusion respecting it ; as the stems in question 

 showed the pith of Artisiae and vessels with bordered pits, it is natural to 

 suspect that they belonged to Cordaiteae. 



To conclude it will be necessary to submit the structure of the leaf- 

 trace-bundles of Sigillaria Menardi and S. spinulosa to further and closer 

 consideration, because Renault in his different publications has made it the 

 ground of some far-reaching conclusions. According to his figures 2 each 

 trace-strand behaves very differently in different parts of its course. 

 Tangential sections through the secondary wood present it in rather 

 oblique tranverse section. It is formed of two evidently separate tracheal 

 groups, between which lie according to the text the spirally thickened 

 initial elements. This would evidently be the so-called diploxylous struc- 

 ture of Cordaiteae. Then in the inner rind the strand assumes much 

 greater unity of character ; the transverse section 3 shows a quite compact 

 apparently homogeneous xylem-strand obtusely triangular in form, in 

 which the spiral tracheides are said in the text to be centrally situated, a 

 little nearer to the outer side. We do not learn from these sections, any 

 more than from those previously mentioned, whether the bundle is colla- 

 teral or concentric. This appears for the first time in a figure in Renault 4 , 

 a tangential section through the Dictyoxylon-layer of the rind which has 

 hit the emerging foliar bundle exactly transversely. The bundle is now 

 broader than before and its transverse section is crescent-shaped and no 

 longer triangular. Its upper inner segment (bois centripete) consists of 

 tracheides lying together in no particular order. The lower outer (bois 

 centrifuge), which was very feebly developed in the previous section and 

 answered to the outwardly inclined apex of the triangular transverse 

 section, is now considerably enlarged, and its tracheides arranged in rows 

 have rays of parenchymatous tissue between-ihem. Next to it the bast- 

 layer is still to be seen in the form of an arch, and as it does not appear 

 elsewhere round the wood, it is evidence of the collateral character of the 

 bundle-strand. We are thus undoubtedly justified in comparing it with 

 the foliar bundle of Cycadeae mentioned above on p. 106 in the chapter 

 on Gordaitae. Reference may also be made to former remarks on Myelop- 

 teris, but Lepidodendreae must for the present be left out of consideration, 

 since observation has led to no direct conclusions in their case, and we are 

 first led to suspect collateral structure in the strand by considerations con- 

 nected with the behaviour of the Stigmariae which we have yet to consider. 



1 Dawson (8). 2 Renault (1), t. n, ff. 18, 19. 3 Renault (1), t. n, f. 20 and (8), 



t- 3> f- '7- 4 Renault (1), t. 12, f. i. 



