10 
PROFESSOR W. C. WILLIAMSON ON THE ORGANIZATION 
figured is probably due to age, since I find that in Angiopteris erecta this layer is scarcely 
visible in the ultimate leaflet-petioles, but is from '004 to ’008 in the secondary rachis. 
In the upper portions of the primary rachis, where the latter has a diameter of about 
three eighths of an inch, this layer has a thickness of about ‘016, whilst near the base 
of the same petiole, where the latter has a diameter of nearly 2 inches, the scleren- 
chyma is nearly -05 in thickness. Similar conditions appear to have prevailed in our 
fossil forms. 
In all the recent examples of Marattiaceous Ferns we have a very distinct ring of 
parenchyma external to the sclerenchymatous cylinder; which parenchyma is often 
more or less completely separated into three layers by the development in its more 
central cells of a quantity of chlorophyl. This superficial parenchyma is very distinct 
in all the species which I have examined, but is the least developed in Marattia 
fraxinea. I have called attention to the existence of indications of a similar layer 
external to the sclerenchyma of some of my fossil examples ; but these specimens have 
not enabled me to detect the epidermal layer, with its stomata-like openings, which 
Professor Renault has found in his well-preserved silicified fragments. 
Whether or not all my fossil examples belong to the same species may be doubtful, 
since they exhibit considerable differences in the diameters of their gum-canals ; but as 
many of these may, as in fig. 4*, have undergone some alteration in size owing to 
contraction of the parenchymatous cells, I think it unsafe, in the present state of our 
knowledge, to make these differences specific features. There are also differences in 
the structure of the sclerenchymatous hypoderm, as shown in figs. 16 Sc 17; but I 
cannot satisfy myself that these differences have more value than the variations in the 
canals. 
The specimens next to be described also belong to the class of Ferns, and are interesting 
because they show that the fossils with which we have so long been familiar from the 
coal-fields of the continent under the general name of Psaronites are not absent from the 
Lower Coal-measures of Lancashire ; but though the evidence I am about to advance 
clearly shows the correctness of the above statement, it must be confessed that our 
representatives of this group of objects present themselves in very humble guise con- 
trasted with the magnificent examples of Psaronius and Protopteris figured in the pages 
of Corda’s ‘ Flora der Yorwelt.’ 
The probable existence of tree ferns in the British Coal-measures was long ago pointed 
out by the late Professor Phillips, and by the authors of the ‘ Fossil Flora of Great 
Britain.’ But these observers derived their conclusions solely from the external forms 
of certain stems. At the Meeting of the British Association for the Advancement of 
Science in 1872, Mr. Carruthers described what he believes to be eight forms addi- 
tional to the two figured in the ‘ Fossil Flora ’ of Lindley and Hutton. All these 
examples appear to have been obtained from the Bath coal-field. Hence I believe that 
the specimens of this group which I am about to describe are the first that have been 
