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XIX. On the Organization of the Fossil Plants of the Coal-measures. — Part VI. Ferns. 
By W. C. Williamson, F.B.S., Professor of Natural History in the Owens College, 
Manchester. 
Eeceived March 18, — Read March 26, 1874. 
In no part of the investigation upon which I have been so long engaged have I encoun- 
tered so many real difficulties as in that of which I am about to lay the results before 
the Society. Amongst the earliest sections which I made I found anomalous structures, 
generally consisting of a single bundle of vessels, such bundles varying much in size and 
form, enclosed in a parenchymatous or prosenchymatous bark. Few of these examples 
exhibited any clear indication of the group of plants to which they had respectively 
belonged. Many of them might have been either Ly copods or Ferns, so far as structure 
was concerned. But in addition to the difficulty of assigning them to their respective 
groups, was the further one of determining which were independent plants or which 
merely varying portions of the same plant. This latter difficulty is more real in the 
case of Ferns than of Lycopods, because nothing is more common amongst the recent 
examples of the ferns than to find a rhizome possessing one structure, its primary 
petiole another, and its secondary and tertiary petioles yet different structures* ; conse- 
quently it became exceedingly probable that similar variations would be found in fossil 
types. This possibility was converted into a certainty by the researches of Cotta, Corda, 
and Renault, all of whom obtained stems with petioles attached, and which exhibited 
differences such as I have referred to. But supposing all these difficulties to have been 
overcome, supposing the disjecta membra of each plant to have been properly collo- 
cated, and each species to have been correctly referred to its natural order, a new 
difficulty arose from the plans of procedure adopted by previous writers on this subject. 
In 1832 C. Bernard Cotta published his 4 Dendrolithen,’ giving descriptions and some- 
what defective figures of a number of specimens to which he assigned new generic and 
specific names. He threw these forms into the three families of Rhizomata, Stipites, 
and Radiati, the latter family being defined as “ Caules ad tertiam familiam perti- 
nentes strias radiales continent, quee horizontaliter perscisste vel inter se separatos con- 
centricos annulos formant, vel inde ab axe incipientes usque ad peripheriam exeunt ” 
* I may observe that, before completing this portion of my inquiries, I made an extensive series of observa- 
tions upon the structure of the rhizomes and petioles of all the recent ferns which I could obtain, especially in 
reference to the way in which the bundles supplying the secondary petioles and nervures originated in the 
primary one. Having thus made myself practically master of a mass of detailed information on these subjects, 
I was enabled to study with the greatest advantage the admirable memoir of M. Tk£cul (“ Remarques sur la 
position des Trachees dans les Fougeres,” Annales des Sciences Naturelles, tom. xii., 5 6me se'rie) and to enter 
upon the present inquiry. 
MDCCCLXXIV. 4 Y 
