736 FOSSIL PLANTS OF THE CAEBONIFEEOUS SYSTEM. 



layer of the bark has arrested the destruction of the entire cylinder, 

 and formed the mould into which inorganic materials have been intro- 

 duced. In Stigmaria, however, the woody cylinder is usually pre- 

 served, probably owing to its more tenacious character. Some think 

 that the stores of fossil fuel in England and America are mainly due 

 to the presence of this plant. Stigmaria ficoides has been shown to 

 be the rhizome and roots of a Sigillaria. Specimens of the latter have 

 been discovered standing erect, and connected with Stigmarias. Stig- 

 maria ficoides abounds in the underclay of a coal seam, sending out 

 numerous roots from its tubercles, and pushing up its aerial stem in 

 the form of a fluted Sigillaria. 



Sigillaria (sigillum, a seal) is another plant which appears to have 

 aided in the formation of coal. It occurs in the form of compressed 

 stems, attaining a height of 40 to 50 feet, and a breadth of 5 feet. 

 The stems are fluted longitudinally, and marked at regular intervals 

 by single or double scars (hence their name), the remains of the leaf 

 insertions (fig. 815). Some suppose Sigillarias to be allied to Tree- 

 ferns, others to Coniferae. Brongniart says they resemble Zamia 

 integrifolia, and appear to predominate in the middle and superior 

 beds of the coal formations. Some consider them as intermediate 

 between Perns and Cyoads. Their foliage has not been accurately 

 determined, some conjecturing that it consisted of Neuropteris, others 

 of long linear leaves, called Oyperites. They have a medullary sheath 

 in the shape of apparently isolated bundles, and vessels interme- 

 diate between true spiral and scalariform. The stem of Sigillaria is 

 fluted in a longitudinal manner, like a doric column, and has a suc- 

 cession of single scars, which indicate the points of insertion of the 

 leaves. When the outer part of the stem separates like bark, it is 

 found that the markings presented by the inner surface difier from 

 those seen externally. This has sometimes given rise to the erroneous 

 supposition that they belong to diflferent genera. King says, that if 

 in imaigination we delineate a channelled stem of any height Ijetween 

 12 and 100 feet, crowned with a pendent fern-like foliage, furnished 

 with wide-spreading thickly-fibrilled roots, and growing in some 

 densely-wooded swamp of an ancient Mississippi, we will then have 

 formed a tolerably close restoration of a Sigillaria vegetating in its 

 true habitat. The fructification consists of small sporangia, like that 

 of Flemingites, borne on the bases of the leaves, and this indicates an 

 acrogenous plant allied to Lycopods. 



Calamites (xaXa/jLog, a reed), a reed-like coal fossil plant, occurs 

 in the form of jointed fragments, originally cylindrical and hollow, 

 but now crushed and flattened (fig. 916). The stem is ribbed and 

 furrowed (fig. 917), articulated and septate. It consisted of a cortical 

 portion now converted into coal, of a medulla, at first solid and then 

 fistular, surrounded by a woody cylinder of scalariform vessels. The 



