CARBONIFEEOUS LYCOPODS AND SPHEN'OPHYLLS. 83 



quincuncial arrangement of the rootlets, which in their arrange- 

 ment are a counterpart of the leaves on the stem. It also differs 

 from typical roots in the structure of the vascular axis and 

 rootlets, which are collateral and not centipetally developed. 

 From a typical rhizome it also differs according to the general 

 acceptation of tliat term, for it has never been shown to give birth 

 to a stem or leaves. It agrees more with a rhizome than a root, 

 in the arrangement of the rootlets and the structure of the 

 vascular axis and the rootlet bundles. Taking, then, the whole 

 circumstances of the case into consideration, Schimper's suggestion 

 is probably the best and only one we are at present warranted in 

 adopting when he asks " if these curious fossils do not represent 

 rather a rhizome than a root."^ The specimen of Stigmaria 

 discovered by Solms-Laubach at Dudweiler, near Saarbruck, 

 which he describes in his Fossil Botany," certainly seems to 

 favour this view. After giving a general description of the fossil, 

 he says, "This specimen is particularly important and interesting, 

 because the appendages appear in tolerably good preservation on 

 both sides of the terminations of the axes. They grow successively 

 smaller and shorter as they approach the terminations, and the 

 distances between them diminish. They also become curved in 

 the forward direction, and close together bud-like round the apex. 

 Hence it is only as they develop that they acquire their definite 

 position at right angles to the axis, resembling in this respect 

 foliage leaves." 



Although, then, in the description of Stigmaria, I have used the 

 terms rhizome and rootlets, it arises from the necessity of having 

 definite terms to apply to these two organs, and as these iwo 

 organs have more the character of rhizomes and rootlets than 

 roots and rootlets, in the absence of any other available descrip- 

 tive word, the former has been adopted. 



Stigmaria is a palaeozoic type of structure which has no 

 counterpart in recent times. 



Note. — In addition to the papers to which reference has already been 

 made, the following may be mentioned : — 



Hooker, Sir Joseph U., "On Some Peculiarities in the Structure of 

 Stigmaria," Altm. Geol. Surveif of Great Briiain, Vol. II., Part 2, 

 p. 431. Plates. 1848. 



1 Schimper, Traiti d. pal^ont. vdgSt., Vol. II., p. ill. 1870. 

 « Solms-Laubach, I.e., pp. 268-269. 



