436 THE CARBONIFEROUS SYSTEM. 



On the genus Syringodendron of Sternberg I have no observations 

 to make. I liave seen only fragments of stems ; and these seem to 

 be very rare. 



I include under Sigillarice the remarkable fossils known as Stig- 

 maria, being fully convinced that all the varieties of these plants 

 known to me are merely roots of Sigillaria ; I have verified this fact 

 in a great many instances, in addition to those so well described by 

 Mr Binney and Mr Brown. The different varieties or species of 

 Stigmaria are no doubt characteristic of different species of Sigillaria, 

 though in very few cases has it proved possible to ascertain the va- 

 rieties proper to the particular species of stem. The old view, that 

 the Stigmariai were independent aquatic plants, still apparently main- 

 tained by Goldenberg and some other palteobotanists, evidently proceeds 

 from imperfect information. Independently of their ascertained con- 

 nexion with Sigillaria, the organs attached to the branches are not 

 leaves, but rootlets. This was made evident long ago by the micro- 

 scopic sections published by Goeppert, and I have ascertained that 

 the structure is quite similar to that of the thick fleshy rootlets of 

 Cycas. The lumps or tubercles on these roots have been mistaken 

 for fructification ; and the rounded tops of stumps, truncated by the 

 falling in of the bark or the compression of the empty shell left by 

 the decay of the wood, have been mistaken for the natural termination 

 of the stem.* The only question remaining in regard to these organs 

 is that of their precise morphological place. Their large pith and 

 regular areoles render them unlike true roots ; and hence Lesquereux 

 has proposed to regard them as rhizomes. But they certainly radiate 

 from a central stem, and are not known to produce any true buds or 

 secondary stems. In short, while their function is that of roots, they 

 may be regarded, in a morphological point of view, as a peculiar sort 

 of underground branches. They all ramify very regularly in a 

 dichotomous manner, and, as Mr Brown has shown, in some species 

 at least, give off conical tap-roots from their underside. 



In all the Stigmaria; exhibiting structure which I have examined, 

 the axis shows only scalariform vessels. Corda, however, figures a 

 species with wood-cells, or vessels with numerous pores, quite like 

 those found in the stems of Sigillaria proper ; and, as Hooker has 

 pointed out, the arrangement of the tissues in Stigmaria is similar to 

 that in Sigillaria. After making due allowance for differences of 

 preservation, I have been able to recognise eleven species or forms 



* For examples of the manner in which a natural termination may be simulated by 

 the collapse of bark or by constriction owing to lateral pressure, see my papers, Quart. 

 Journ. Geol. Boc, vol. x. p. 35, and vol. vii. p. 194. 



