210 
PROFESSOR W. C. WILLIAMSON ON THE ORGANIZATION 
fig. 27, k) of the subepidermal layer, whilst beyond this again the outermost epidermal 
parenchyma reappears and composes the bases of the leaves (Plate XXVI. figs. 24 & 27, l). 
These petioles present the usual appearance of such appendages. Plate XXVIII. fig. 28 
represents a tangential section of them, close to the surface of the epidermis. The trans- 
verse diameter of each cicatrix is fully three times its vertical one ; in other respects 
these petioles are undistinguishable from those of the Lepidodendra already described. 
Fig. 24, shows that the extremities of the petioles are compressed and membranous, 
whilst their bases (fig. 24, I) are turgid. One striking feature of this plant is the great 
apparent thickness of the mass of persistent petioles, as indicated by the lower portion 
of fig. 24, all external to the dark line of tubular prosenchyma (k) being an aggregation 
of these appendages. So far as all these portions of its organization are concerned this 
TJlodendron resembles the lowest types of Lejridodendron. 
The remarkable circular areolae of TJlodendron arranged in two vertical rows, one on 
each side of the stem, are sufficiently distinct in this specimen ; they have each a dia- 
meter of more than an inch. But sections through them exhibit no peculiarity of 
structure beyond the circumstance that, in this specimen, the epidermal layer is absent 
from their superficial area*. The margin of the band of tubular prosenchyma (k) forms 
their outer boundary line, whilst their superficies is occupied by the middle bark. In 
one instance I have discovered indications of a vascular bundle running to the centre of 
the areola, but it is too indistinct to be of much value. It seems probable that these 
scars sustained objects which were chiefly developed from the epidermal layer, and whose 
bases rested upon the outer bark ; they certainly were not roots or branches, and I 
incline to the belief that they were organs of fructification. 
Amongst numerous other specimens for which I am indebted to Mr. Whittaker, of 
Oldham, is a small but very well-marked fragment of Favularia , with the characteristic 
square cicatrices of full size and remarkably prominent. The specimen had been sub- 
jected to great pressure; consequently the subepidermal layers of the two sides had been 
brought into the closest contact, whilst the central axis, along with detached fragments 
of the prosenchyma, had been squeezed out from between the contiguous cortical layers. 
Unfortunately I did not obtain a good transverse section of the medullary axis and 
ligneous zone, having only discovered their presence by finding them in two of my 
longitudinal sections. The latter, however, show them with some distinctness. Plate 
XXVII. fig. 29 exhibits a longitudinal section of three of the epidermal leaf-scars ( l ) 
with a fragment of the central axis in almost its normal position, the greater part of 
the cortical prosenchyma, which ought to have intervened between the two, having been 
forced out of its place. Plate XXVIII. fig. 30 is a transverse section of two of the leaf- 
scars and the subjacent prosenchyma. Fig. 31 is a radial longitudinal section of one 
portion of the central axis to the right hand of fig. 29, including part of the medulla, 
all the ligneous zone, and a little of the cortical parenchyma. Fig. 32 is a longi- 
tudinal section of the epidermal layer, showing the transition from the regular paren- 
* The specimen has been weathered or watered over, which may possibly account for the absence. 
