184 DR. HARLEY ON THE PARASITISM OF THE MISTLETOE. 
streaming of the sap, first of all, out of the wood-layers which are in process of formation, 
and certainly also out of those which are already formed." In the figure the fibro-vascular 
bundles of the nourishing plant are represented curving towards the sides of the root, 
against which their extremities abut at various angles. This appearance is occasionally 
seen, but I believe that it is produced by the absorption of the fibro-vascular bundles 
about the angles of convergence or of divergence, in the extension of the root in these 
directions, and therefore to be independent of any tendency to inosculation of the 
ducts. 
That the vessels of the two plants do not, however, directly inosculate, as is represented 
by Unger, and that their inosculation is probably accidental and contingent upon the 
relation of the parenchymatous systems of the two plants, will, I presume, be evident 
from the following facts :— 
1. The reticulated ducts of Viscum album invariably run parallel to the surface of the 
part in which they are contained. It has been shown that the vertical roots of Viscum 
run horizontally inwards parallel to the medullary rays, and therefore at right angles to 
the fibro-vascular bundles which regularly diverge around them. In longitudinal sections 
of these roots it is readily and uniformly observed that the reticulated ducts run parallel 
with the long axis of the root, and rows of the long reticulated cells which compose them 
frequently occupy the surface of the root, and come into contact with a wall formed 
of wood-fibres and ducts in transverse section (Pl. XXX. fig. 17). Here, then, it is 
clear that the vascular tissues of the two plants are arranged at right angles to each 
other. 
2. If, now, we take a section of the conjoined tissues from the edge of a vertical plane 
which would bisect the woody base of the parasite (Pl. XXX. figs. 20 & 18), and 
where the ducts of the two plants would be supposed to run in the same linear directions, 
we shall find that they actually do so to within a short distance of the line of junction, 
but that here the ducts of Viscum, having changed their direction, as above described, 
appear in transverse section, in which condition they abut against the abrupt ends of the 
fibro-vascular bundles of the nourishing plant, which are here, even near the median 
plane, a little inclined in their divergence about the base of the parasite, to the right or 
to the left. Again, in sections at right angles to that just described (Pl. XXX. fig. 19), it 
is observed that the ducts of the Mistletoe, having run parallel to the surface of the base 
of the parasite to within a very short distance of the line of junction with the nourishing 
plant, suddenly bend inwards in order to become parallel with the surface of the 
tapering’ root, in which they all in like manner converge. In the position therefore 
which is of all most favourable for the direct inosculation of the vascular bundles, we 
find that they are still arranged at right angles to each other. That they do frequently 
inosculate, however, is quite certain; but the circumstance of their doing so appears, as 
I have stated, to be a necessary consequence of the confluence of the medullary systems 
of the two plants. Thus, in the former of the two sections (Pl. XXX. figs. 18 & 20) 
just described, it is observed that the base of the parasite near the line of junction is 
chiefly composed of parenchymatous tissue (in part thick-walled and dotted cells, and in 
part of thin-walled unchanged cells) (Pl. XXX. fig. 19) subdivided into large medul- 
