3 86 STIGMARIA. 



is developed at the base of a dichotomy, as the roots are developed beneath 

 the place where the stem branches in Selaginella. From this we may at 

 least conclude that these conical bodies are not objects of casual occurrence, 

 but that they stand in some distinct though not yet determinable relation 

 to the structure of the stem. 



If now from all the circumstances which have been discussed there can 

 no longer be any doubt that Stigmariae are simply members of stems of 

 Sigillarieae and Lepidodendreae which performed the functions of roots, 

 and that they must be removed from the system as a distinct group of 

 plants, yet a few further facts connected with the positions in which they 

 are found may be brought forward in confirmation of this view. It has 

 long been known that in Westphalia, in England, in Canada and elsewhere, 

 the floor of the coal-seams is usually formed of beds of clay of varying 

 thickness, which are traversed by countless Stigmariae. These beds are 

 called in England Stigmarian underclays. These Stigmarias appear in 

 general to have no connection with the seam of coal, but Grand' Eury 1 tells 

 us that he has observed a direct transition of the kind at Dombrowa in the 

 coal-field of Poland and Upper Silesia. That the plants must have grown 

 in the substance of these beds of clay is shown by the arrangement of their 

 appendages already noticed by Lindley and Hutton 2 ; when the appendages 

 spread on all sides at right angles to the axis they lie parallel with the 

 bedding, but when they are directed upwards or downwards they are at 

 right angles to it. Consequently, if they grew so luxuriantly in the mud 

 of the Carboniferous swamps on the surface of which the formation of coal 

 began, they cannot well have been organs of assimilation, but must have 

 been adapted rather to take up material from the substratum. They are 

 distributed in like manner through the roof of the seams, but are not so 

 abundant there, and they seldom reach the level of the coal itself but are 

 separated from it by a layer, though often only a thin layer, of the clay. 

 This is intelligible, if we consider that a certain time must have elapsed 

 before a fresh vegetation of Stigmariae could commence on the mud which 

 covered the Carboniferous swamp, and which was deposited through the 

 irruption of streams of water from other quarters. As they were safe in 

 their mud from being floated away by running water, it was easier for the 

 cylindrical axes when once formed to remain in their natural position, and 

 therefore it is that they are found so abundantly in the case of Stigmariae, 

 while those of the stems both of Sigillarieae and Lepidodendreae are of 

 rare occurrence (see on p. 265). 



Further, the study of the seams themselves and of the calcareous 

 nodules sometimes present in them gives occasion to similar considerations. 



1 Grand' Eury (2), p. 151. a Lindley and Hutton (1), vol. ii, Introd. 



