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and on the other hand that some really different plants have 
been united under a single species. 
• The plants which have contributed most largely to the 
formation of the coal, are those included in the genus Sigillaria. 
Their fluted trunks and tuberculated roots are among’ the first 
fossils that a student observes in a visit to a coal field. The 
roots ( Stigmaria ) were long a puzzle to botanists. They were 
observed to proceed from a large central and apparently perfect 
66 cup or dome,” and, dichotomously dividing, they extended to 
a great distance in the shale in which they were preserved 
in a singularly perfect condition. Lindley and Hutton, after 
examining several perfect specimens, as they supposed, during 
the progress of their “ Fossil Flora,” gave up their original 
opinion, that it was a prostrate land plant, and considered it in 
the end, as a huge aquatic plant, growing on the soft mud at 
the bottom of still lakes. Brongniart, from a consideration of 
the structures of the two genera, suggested that Stigmaria 
might be the root of Sigillaria ; but the first step to a positive 
determination of the true nature of the plant was made by Sir 
William Logan, when he observed in the South Wales coalfield 
that every bed of coal rested on a layer of under clay, which was 
full of Stigmaria , and the relation suggested by Brongniart 
was established by Mr. Binney, who traced the connection 
between the sigillarian trunk and the stigmarian roots in a 
quarry at St. Helen’s, in 1843. 
The supposed leaves which are given off by the roots through- 
out their whole course and from every portion of their circum- 
ference, are rootlets composed entirely of cellular tissue, except 
a slender bundle of vessels which passes through them. These 
rootlets have been traced to a length of twenty feet. 
Although specimens of Sigillaria are so abundant, they are 
so imperfect that less is known of this genus than of almost any 
of the other coal plants. It is doubtful whether the trunk was 
simple or branched, and whether the foliage was composed of 
linear leaves or fernlike fronds, and nothing whatever is known of 
its fructification. It is consequently not to be wondered at that 
very different notions have been entertained of its systematic 
position. By Lindley and Hutton, and by Cordau, it was re- 
ferred to Euphorbiacece , by Schlotheim to palms, by von Martius 
to Cacti , by Sternberg to ferns, by Brongniart to a position in- 
termediate between Lycopodiacece and Cycadece , by Hooker to 
Lycopodiacece , by Dawson to Cycadece , and lastly, Groeppert who 
has spent a long life in the study of fossil plants, writes, within 
the last few months, that its true position has not yet been 
determined. 
Both Brongniart and Binney have described the internal 
structure of supposed species of Sigillaria , but the external 
