164 
PROFESSOR W. 0. WILLIAMSOR ON THE ORGANISATION 
enclodermal cells, o. Numerous thin vertical plates, d, chiefly but a single row of 
cells in thickness, radiate from the zone c to the thicker peripheral one f, encircling 
numerous large, radially-disposed lacunae. Every feature of this apparent root 
reminds us of the structure of the cortex of Asteropkyllites Williamsonis, described in 
my memoir. Part XII.* Whether or not the two belong to the same plant cannot at 
present be determined. The specimen, which is from Halifax, may be named 
Rhizonium lacunosum. 
Index to the Plates, 
Plate. 
1 
Fig. 
Pages on whicli 
references are i 
made to the 
figures. 
! I 
1 
i 
1 
i 
1 
Rachiopteris Grayii, with transverse section of the 
vascular axis and some of its appendages : a, medul¬ 
lary parenchyma; a, five radial extensions of the 
same; h, vascular axis ; h', end of the ray, h" of &, 
detached to form the vascular centre of a lateral 
appendage ; c, a band of an apparently structural 
tissue, but possibly an only result of mineralisation ; 
d, numerous appendages, probably adventitious root¬ 
lets, Number which the specimen figured bears in my 
Cabinet, 1832. XlO. 
! 
i 
156 1 
I 
2 
A second section somewhat similar to fig.l; //, the cylin¬ 
drical axis of lateral organ, c, as in e, fig. 3. Cabinet 
number, 1833. XlO. 
i 
156 
1 
3 
Part of a section resembling 1 and 2, including a 
Zygopteroid petiole : f, the central part of its vas¬ 
cular bundle ; d, a zone investing the vascular 
bundle of the petiole identical in its nature with 
that investing fig. 1 at c; c, a cylindrical appendage 
like fig. 2, 6 ; d, d, rootlets; g, black carbonised 
cortical tissue. Cabinet number, 1831. X 9 
156 i 
1 
4 
Section of a well preserved Zygoj)teroid petiole, like 
fig. 3 : f, the central bar of its vascular bundle; 
f', f", its transverse bars; c, an investment of the 
i 
* ‘ Phil. Trans.,’ 1883. 
