180 DR. HARLEY ON THE PARASITISM OF THE MISTLETOE. 
When the root of the parasite begins to increase in diameter by the formation of 
woody layers, the fibres and ducts of the nourishing plant, leaving their strictly vertical 
direction, incline outwards towards the base of the Mistletoe, and the woody layers of 
the two plants ultimately become coincident, and have the same relation to each other 
as have the woody layers of the trunk of a tree to its horizontal branches, but with this 
difference, the woody layers of the nourishing plant are not simply coincident with those 
of the Mistletoe, but, at their junction with them, are pushed outwards on all sides of 
the growing base of the parasite; so that, in transverse or in longitudinal sections 
parallel to the medullary rays (Pl. XXIX. fig. 12), the fibres and ducts in the imme- 
diate vicinity of the parasite are divided more or less obliquely. "This explains the 
appearances seen in Pl. XXX. fig. 19, where the wood-cells and ducts of the Poplar 
are represented, not only divided a little obliquely near and at the line of junction with 
the base of the parasite, but also laterally divergent, This divergence of the woody 
layers is effected in a very regular way in the Maple: they are not bent bodily outwards 
in a simple curve from around the root, but each layer is separately bent away from it 
at the lines where the wood-rings encircle the sloping surface of the woody base of the 
parasite, and so suddenly as to cause ridge-like elevations corresponding in number and 
position to the concentric rings of the wood of the nourishing plant. These successive 
outward bendings of the woody layers commence at that part of the root which first 
begins to enlarge, and progressively increase as they affect the outer layers. Thus is 
explained the formation of the circular ridge-like elevations occurring on the walls of 
the conical cavities occupied by the roots of the parasite, to be described hereafter. 
The roots of the Mistletoe are very perishable, and after the death of the stock 
they soon crumble down in the hard woody cavities which contained them, giving 
to the surface of the decorticated branch an alveolated appearance. The alyeoli 
are arranged in linear series along the branch, but when crowded the rows become 
confused. They have a superficial resemblance to the alveoli of the human jaws, and, 
like those which receive the double teeth, they sometimes present partitions below. 
These branched alveoli result from the confluence of the roots at their bases, while the 
extremities have remained distinct, and therefore contained in separate cavities. The 
cavities which correspond to the larger woody roots are almost always branched towards 
their apices, each one dividing into two or more separate canals. 
In the Maple the sloping walls of the cavities which contained the older roots are 
striated longitudinally by fine linear elevations of the wood, and marked transversely a 
pretty regular intervals by circular tidges corresponding in number and position with the 
concentric rings of the wood. Dr. Hooker has noticed the same appearance in the conical 
cavities left in the wood of Fagus after the falling away of the parasitic Myzodendron. 
He says (‘Flor. Ant.’ pt. ii. p. 301), “The parasite falls away, and leaves a cup still 
terminating the branch of Beech, whose inner surface is channelled with radiating fissures; 
and these again crossed by the concentric rings of the wood.” I have already explaine 
how these circular elevations are produced in the Maple. ET 
` The longitudinal striations are best seen at the bases of the cavities: they are not visible 
at the apices of any. P REA 
