IX. 



The Relationship of the Carboniferous Plants, 

 Sigillaria and Stigmaria. 



T^HE true nature of Stigmaria has long been a fruitful subject of 

 discussion among palaeophytologists, Brongniart, who appears 

 to have first established and defined the genus, describes the speci- 

 mens so named as stems bearing leaves, which ultimately disarticulated 

 and left the surface marked by scars arranged in a quincuncial order.' 

 He seems to have had some knowledge of the internal structure of 

 Stigmaria, and on the strength of this and other features placed it, 

 with some reservation, amongst the Lycopodiaceae, pointing out that 

 it had many points of analogy with the existing genus Isoctes, and 

 suggesting that it might be considered as a gigantic aquatic Lycopo- 

 diaceous plant, in fact, a sort of arborescent Isoctes. The subsequent 

 discovery by Binney and others of fossil Sigillariis and Lepidodendva, 

 whose trunks were continued downwards at the base into large, 

 spreading, and bifurcating structures recognisable as Stigmayia^,- soon 

 gave rise to another view of their morphological nature, viz., that 

 they were in reality the roots of these trees, and not the stems of 

 independent plants as had been generally supposed. From that 

 time to the present, opinions have been divided as to which of these 

 two views was the correct one, and as new facts have been brought 

 to light, the advocates on either side have sought to interpret them 

 in accordance with the opinions they hold. After carefully weighing 

 the whole of the evidence available five years ago, Count Solms- 

 Laubach came to the conclusions that the best explanation of the 

 known facts was to be found in the hypothesis that the Stigmaria 

 were rhizomes adapted to a soft pulpy environment, whose appen- 

 dages, though probably foliar in their nature, were functionally 

 organs of absorption. 



On the assumption that this conclusion was correct, the further 

 question presented itself as to how the aerial Sigillaria with its 

 Stigmarian rhizomes was developed. Was it to be supposed that 



1 " Prodrome d'une Histoire des Vegetaux fossiles," 1828. 



2 For details of these discoveries, &c.; see Williamson, Stigmaria ficoides, Palaonto 

 graphical Society, 1887 ; also Solms-Laubach, " Fossil Botany," Clarendon Press. 



<* " Fossil Botany," pp. 291-293. 



