438 STRUCTURE OF STIGMARIA. 



theory of Stigmaria being a root. We know, however, very little of 

 the roots of living plants, their importance in systematic botany being 

 trifling. There is, however, no good cause for supposing that symmetry 

 should not pervade the subterraneous as well as the superior organs of 

 plants ; and in the case of the roots of some Palmce in common use, 

 but of unknown origin, we have an arrangement of rootlets round a 

 prostrate root (analogous to the root of Stigmaria), as symmetrical as 

 in Stigmaria itself. 



M. Goeppert has recognised, in the majority of those species of Stig- 

 maria which are founded on variations in the form and disposition of 

 the sexes, only one. That such a view is concurrent with the fact of 

 the genus representing merely a root, is obvious ; for such an organ 

 cannot be expected to afford specific characters. M. Corda, on the 

 contrary, has given the name of Stigmaria jicoides to the dissection 

 of a plant which evidently bears no very close relationship to the cha- 

 racteristic fossil of our British under-clay, and which is, doubtless, the 

 true S. jicoides of authors. M. Corda's S. jicoides is, on the other 

 hand, possibly a stem, and not a root. 



There are in the Museum of Practical Geology so many Stigmaria 

 specimens, the majority having only the external characters preserved 

 (though in not a few the internal tissues, and in some both, are admira- 

 bly displayed), that I can confidently affirm, that specimens figured by 

 Corda (Tab. XII.), do belong to the same genus, and probably species, 

 as M. Brongniart's dissections in the Archives. In proof of tbis asser- 

 tion I would adduce the figures and dissections of Plate 2, Bot. figs. 

 5 — 13, all having been made from the one specimen, fig. 4. 



Explanation of Plates. 



Plate 1, figs. 1 and 2. Two views of a specimen of Stigmaria, 

 fossilized without compression, and showing the pits or cavities from 

 which the rootlets emerge in an unmutilated condition. The bases 

 of these rootlets are generally retained within the cavity. Specimen 

 from Peel Quarry, Lancashire, above the white-coal seam, — Mr. 

 Ormerod's cabinet. Fig. 3, specimen of a similarly preserved fossil, 

 from the cabinet of Miss Jukes, of Birmingham. 



Plate 2, fig. 1, rootlet of Stigmaria Jicoides. Fig. 2, horizontal 

 section of ditto, very highly magnified, showing at a the position of 

 the vascular axis. Fig. 3, cellular tissue from ditto, more highly 

 magnified. Fig. 4, portion of Stigmaria Jicoides, showing the scars as 

 they usually appear, and enclosing an axis from which the dissections 

 5 — 13 were taken. Fig. 5, horizontal section of axis in fig. 4, of 

 natural size. Fig. 6, posterior ends (those towards axis) of the vas- 

 cular tissue (b) forming the wood, divided by broad and narrow medul- 



