a New Fern from the Coal-Measures . 2 1 1 
surface of the petiole, is probably, to a large extent, the result 
of shrinkage and separation of the tissues; the dark line 
bounding the larger tracheids shows the position of a few 
crushed thin-walled cells. In Fig. 5 another of the smaller 
bundles is shown, but here there is no vacant space ; by far 
the greater part of the bundle consists of tracheids, and on 
the side facing the surface of the petiole a group of narrower 
elements marks the position of the protoxylem. Intermixed 
with the tracheids are small parenchymatous cells ; surrounding 
the xylem is a narrow layer of thin-walled and crushed elements. 
On carefully examining the tissue which, in the figure, 
seems to be in immediate contact with the xylem, there may 
be noticed at c , c two oval spaces ; similar spaces occur round 
the entire circumference of the bundle ; these are the small 
and characteristic canals already alluded to as one of the chief 
features of Rachiopteris Williamsoni. 
In Fig. 6 a third example of the smaller bundles is repre- 
sented ; there is the same kind of space here as in Fig. 4, and 
the small protoxylem-elements are clearly defined. The chief 
point of interest of this figure lies in the small canals, appa- 
rently in different stages of development, shown at £ vii , c viii , c ix ; 
these will be examined more closely after describing the larger 
form of vascular bundle. 
Fig. 7 shows one of the larger and more central vascular 
bundles; the xylem-tracheids and xylem-parenchyma are 
clearly defined ; completely surrounding these we have a band 
of thin-walled tissue largely consisting of elongated narrow 
elements, and evidently constituting the phloem ; at the outer 
edge of this tissue there are the characteristic canals placed at 
regular intervals, and at c m -c yi they seem to be in similar 
early stages of development to those of Fig. 6. The position 
of the protoxylem-group is shown at /, and at p 1 ; the small 
size of the elements opposite the larger space suggests a second 
group of protoxylem. The two spaces are in all probability 
the result of tissue separation. In this, as in all the bundles 
of the petiole, there are no indications of a definite endo- 
dermal layer. The largest and most perfectly preserved 
