DR. HARLEY ON THE PARASITISM OF THE MISTLETOE. 195 
have been made, and for having pointed out to me, in Oakley Park, near that town, a 
clump of fine Maples affected in the way I have described. As we were walking, in the 
spring of the present year, through this wild and beautiful park, we came to the stump 
of a Maple, six feet high, and between two and three feet in circumference. To one side 
of it was still attached one of its large primary branches, but it was withered and nearly 
dead. The cause of the destruction of this tree was sufficiently apparent: round about 
were strewn portions of its dead decorticated branches, here and there swollen and per- 
forated by roots of the Mistletoe. The solitary attached branch, enormously swollen near 
its base, and thickly beset with Mistletoe, was fast rotting away, while the parasite still 
flourished in the little living bark that remained about its junction with the trunk. 
LÀ 
EXPLANATION OF THE PLATES. 
Prate XXVIII. 
Figs. 1, 2,3. Cross sections of branches of Maple (Acer campestre) infested with Mistletoe (Viscum album). 
The branches are hypertrophied to thrice their natural size, and the bark is proportionately 
. thickened, the outer layers being dead and deeply fissured. The taper cellular roots of the 
parasite are seen converging inwards from all parts of the circumference. The centre parts 
of the wood are dead. 5, b, b, woody roots with soft taper prolongations ; a, a, a, dead roots. 
Fig. 1 a, fig. 2 a, completely buried in the wood. Fig. 3 a, a large woody root in process of 
being buried. pig 
Figs. 4, 5, & Pl. XXIX. fig. 6. Longitudinal sections of a branch of Maple, made in a direction parallel, 
or nearly so, to the medullary rays. Fig. 4 represents a young plant situated in the hyper- 
trophied bark, and sending down vertical roots towards the wood, and horizontal ones between . 
the layers of the bark, illustrating the way in which the outer layers of the bark are separated 
from the living layers beneath them. Figs. 5 & 6 show the longitudinal course of the 
lateral roots in the bark, and the production of secondary roots and stems from them. The 
vertical roots in this section are observed to be parallel to each other, and to be wider than 
when seen in cross sections of the nourishing branch. 
PLATE X XIX. 
Fig. 7. Section of a similar branch of Maple made at right angles to the medullary rays, showing the 
roots of the parasite in transverse section. Those about the centre of the figure are seen to be 
enveloped by dead wood. Some have crumbled away and left channels. 
Fig. 8. Cross section of a branch of Hawthorn (Crategus ozyacantha) hypertrophied to about three times 
its natural thickness. The conical woody base of the Mistletoe is prolonged into a cellular 
root, which terminates at the central pith. The divergence of the woody fibres of Crategus, 
and the coincidence of the woody layers of the two plants, are well seen: a, two roots curving 
in correspondence with the-medullary rays. 
Fig. 9. Cross oi of a dead branch of e oxyacantha, which has been much infested with 
; Mistletoe: a, Viscum album. The extreme divergence of the woody fibres, and the grooving 
of the stem by the arrest of its development in the direction of the dead roots and its 
hypertrophy in connexion with those which have lived subsequently, are here shown. The 
dark radiating lines indicate the position formerly occupied by roots of the parasite. 
