246 THE GROWTH OF COAL 



Mention has been made of Sigillaria and other trees of the 

 coal formation period. These trees and others allied to them, 

 of which there were many kinds, may be likened to gigantic 

 club mosses, which they resembled in fruit and foliage, though 

 vastly more complex in structure of stem and branch. Some 

 of them, perhaps, were of much higher rank than any of the 

 modern plants most nearly allied to them. One of their most 

 remarkable features was that of their roots those Stigmariae, 

 to which so frequent reference has been made. They differed 

 from modern roots, not only in some points of structure, but 

 in their regular bifurcation, and in having huge root fibres 

 articulated to the roots, and arranged in a regular spiral 

 manner, like leaves. They radiate regularly from a single stem, 

 and do not seem to have sent up buds or secondary stems. 

 They thus differed from the botanical definition of a root, and 

 also from that of a rhizoma, or root stock ; being, in short, a 

 primitive and generalized contrivance, suited to trees them- 

 selves primitive and generalized, and to special and peculiar 

 circumstances of growth. Some botanists have imagined that 

 they were aquatic plants, growing at the bottom of lakes, but 

 their mode of occurrence negatives this. I have elsewhere 

 stated this as follows : 1 



" It is quite certain that Stigmariae are not * rhizomes which 

 floated in water, or spread themselves out on the surface of 

 mud.' Whether rhizomes or not, they grew in the soil, or in 

 the upper layers of peaty deposits since changed into coal. 

 The late Richard Brown and the writer have shown that they 

 grew in the underclays or fossil soils, and that their rootlets 

 radiated in these soils in all directions. 2 In one of my papers 

 I have figured a Stigmarian root penetrating through an erect 

 Sigillaria, and Logan, in his Report of 18^5, had already 



1 Natural Science, May, 1892. 



2 Quart. Journ. Geol. Soc., vol. ii. p. 394 (1846) ; Ibid., vol. iv. p. 47 

 (1847) ; Ibid., vol. v. p. 355 (1849); Ibid., vol. v. pp. 23, 30. 



