698 
PROFESSOR W. C. WILLIAMSON ON THE ORGANIZATION 
horizontale du faisceau vasculaire, au lieu d’etre simples et formees d’une seule ligne de 
faisceaux, paraissent divisees en deux lames, formees de vaisseaux de grosseurs tres- 
differentes et separees par du tissu cellulaire assez mal conserve ; ces deux bandes se 
rejoignent par leurs extremites ” (loc. cit. p. 171). It is the loop-like continuity of the 
parallel bands of large and small vessels at each of their extremities that constitutes 
the characteristic feature of this plant. In the specimen which I have figured this 
arrangement is well shown at the lower end of each of the vertical arcs seen in the 
transverse section of the bundle. At the upper extremity of the arc to the right this 
arrangement has been disturbed by the accidental detachment of the fragment ( aa ). 
The innermost cortical layer (g) is much better preserved in my specimens of this 
species than in those of Z. Lacattii, though partial desiccation or some similar dis- 
turbing agency has caused much of it to disappear and thus interrupted its continuity. 
In the upper part of the section about one fourth of it has so disappeared, and even in 
the remaining portion a ring of large lacunae exists in it, which obviously did not 
characterize the plant in its normal state. It consists of a delicate parenchyma. In 
the vertical section (Plate LYIII. fig. 50) its cells ( g ) are seen to be arranged in the 
irregular vertical columns so common amongst Cryptogamic plants. This tissue 
evidently corresponds closely with that observed by M. Renault occupying a similar 
position in Zygoyteris Lacattii , only in the latter plant numerous lines of vertically 
elongated cells exist — supposed by M. Renault to be reservoirs of gum, but of which I 
find no trace in the specimen under consideration. The middle and outer barks 
correspond closely with those of Z. Lacattii. At h we have the more strongly marked 
middle parenchyma, consisting of cells with much thicker walls than occur in the inner 
bark ; but, as in the latter, they are arranged in irregular vertical lines. On approach- 
ing the surface of the petiole this parenchyma rapidly passes into the prosenchyma (Jc) 
which forms the thick outermost layer of the bark. 
The latter tissue exhibits one feature not described by M. Renault, and which I have 
not observed in any of my specimens of Z. Lacattii. Both the longitudinal and trans- 
verse sections are furnished with a number of conical protuberances (figs. 49 & 50, L), 
which are obviously abortive hairs. Transverse sections of these hairs have a perfectly 
circular outline, and show them to consist of some of the thick-walled prosenchymatous 
cells of the outer bark deflected outwards. They are evidently of the same nature as 
the appendages already described in connexion with Plate LII. fig. 13, and similar 
though smaller examples of which abound on the petioles of the living Pteris umbrosa , 
only from their size and strength in the plant under consideration they must have 
resembled blunted spines. 
None of the writers who have described examples of Corda’s genus Zygojpteris have 
entertained the least doubt that the plants included in it were petioles of ferns ; and my 
investigations have led me to the same conclusion. The discovery, both by Cotta and 
M. Renault, of stems to which, in some instances, these petioles were attached, led me 
to search diligently amongst the nodules of the Oldham two-foot coal, in hopes of 
