212 
PROFESSOR W. C. WILLIAMSON ON THE ORGANIZATION 
epiderm in the longitudinal section, but I find them in the tangential section of the latter 
tissue. 
From the above description it will be obvious that though Favularia has its own 
peculiarities, especially as seen in the varied character of the cells constituting the me- 
dullary axis, and in the apparent though not certain absence of all medullary vessels, 
its general structure indicates its close affinity with the Lepidodendroid plants ; we have 
in both the same thick prosenchymatous bark with its thin tubular layer at the inner 
surface of the epiderm passing into the regular parenchyma of the petioles. These facts 
are important because of the obscurity which yet rests upon the history of the true 
Sigillarise. No one has questioned the close affinity of Favularia and Sigillaria : the 
very prominent cicatrices of the former are but exaggerated representatives of the slightly 
projecting leaf-scars of the latter. 
A remarkable specimen of Favularia , which appears to have borne cones, will be 
described in the sequel of this memoir. 
Considering the abundance of Sigillariae in the Coal-measures, it is marvellous that 
indisputable specimens displaying their internal organization should be so rare ; but such 
is the case. After years of search I have only met with three specimens, of the Sigillarian 
character of which there can be no doubt. One of these is a portion of the epidermal 
layer, with five of the parallel flirtings that characterize the genus, each of the depressed 
ridges having a breadth of nearly three eighths of an inch, the distance between the 
central point of one areola and of that adjoining it being rather more. On the external 
surface the grooves separating the prominent ridges follow a slightly wavy course, as in 
the Sigillaria contracta of Brongniart and several other species ; but at the inner surface 
of the epiderm, where there are corresponding longitudinal projections, the latter are in 
straight lines, explaining the difference so commonly observed in the Sigillaria3 found in 
the coal-shales between the outer surfaces and the so-called decorticated portions ; the 
latter are, as I have already shown to be the case among the true Lepidodendra, casts 
of the inner surface, not of the bark, but of its epidermal portion, which has been held 
together by the firm layer of bast-tissue that occupies its inner surface. 
The structure of what remains of this specimen is very similar to that of the one last 
described. Plate XXIX. fig. 35 is a transverse section, enlarged four diameters, of four 
of the ribs, the outer surfaces of which project into the stone. Fig. 36 represents one of 
these, magnified thirteen diameters. The external portion (/) consists of very regular 
parenchyma, which becomes exceedingly dense at its outer surface ; but internally these 
cells assume a radiating linear arrangement, a circumstance to which I shall again call 
attention when speaking of the structure of Stigmaria. Still more internally (i) we 
have smaller prosenchyma arranged in the usual radiating lines. On turning to the 
longitudinal sections, Plate XXVIII. figs. 37 & 38, the latter of which is a more highly 
magnified representation of a portion of the former, we have precisely the outline which 
a corresponding section of an ordinary Sigillaria would present. . The depressions (l) in 
the outline represent the lozenge-shaped scars left by the deciduous petioles, whilst l ' are 
