216 
PROFESSOR W. 0. WILLIAMSON ON THE ORGANIZATION 
Hooker, and Binney have such distinctive features that they ought not to be mistaken 
for any other. I shall now proceed to show what those features are. I must add that 
for some of the most remarkable specimens which have enabled me to throw additional 
light upon this subject, I have been indebted to Messrs. Nield and Whittaker, of 
Oldham. Others have either been furnished by Mr. Butterworth, or found by myself. 
Of the figures accompanying this memoir, Plate XXX. fig. 43 is a portion of a longi- 
tudinal radial section of a part of the woody cylinder at its inner or medullary surface. 
In this figure, n is a vascular bundle passing outwards through a large medullary ray. 
Plate XXIX. fig. 44 is a corresponding section of the outer part of a similar cylinder. 
Plate XXIX. fig. 45 is a tangential section from the interior of the woody cylinder, 
revealing one large or primary, and numerous smaller or secondary medullary rays. 
Pig. 46 is a still more enlarged section of part of fig. 45, with two vessels and several 
secondary medullary rays. Plate XXX. fig. 47 is a transverse section of part of the 
medullary or inner portion of the woody axis, with a primary medullary ray and a vascular 
bundle going off to one of the rootlets. Fig. 48 is part of the external surface of the 
ligneous cylinder. Fig. 51 is a transverse section of part of the epiderm with the 
attached bases of three rootlets. Plate XXXI. fig. 52 is a further enlargement of 
another rootlet with the epidermal layer from which it springs, and fig. 53 is a diagram- 
matic restoration of the entire plant. Each of these structures requires to be examined 
in detail. 
Several of the specimens which I have examined exhibit more or less of the 
medullary axis, especially one given me by Mr. Whittaker, of Oldham. It consists 
of delicate parenchyma, which is better preserved where it is in contact with the ligneous 
zone (Plate XXX. figs. 43 & 47, a) than in the more central portions, where it has been 
more liable to become disorganized from some unknown cause. The cells have a 
diameter of from - 005 to *0025. There is not a trace of any spiral or barred structure 
in the cell-walls, nor of any medullary vessels such as are common in many of the Lepi- 
dodendroid stems. 
The woody zone consists, as is well known, of a cylinder of radiating wedges which 
increase in size from within outwards. These wedges are composed of large barred 
vessels arranged in radiating lines, and in the most regular order. The external surface 
of the zone, as seen in one of Mr. Whittaker’s fine specimens, is represented in Plate 
XXX. fig. 48, which exhibits a disposition of the structures recurring in every tangen- 
tial section made from any part of the woody cylinder, and which disposition is one 
essential characteristic of a true Stigmaria. The woody wedges (fig. 48, e ) alternately 
approximate and diverge, leaving, in the latter case, large lenticular spaces (f) filled 
with muriform cellular tissue passing straight through the entire ligneous zone, and 
which are the medullary rays of Broxgniart and Hooker. The vessels (e) have a 
diameter which varies from "0025 to ’005. On making a tangential section like 
Plate XXIX. fig. 45, we see that the lenticular orifice is a large medullary ray (/'), 
which maybe distinguished by the name of primary. It consists, as seen in the section, 
