208 MISTLETOES AND LORANTHUSES. 
sinker itself remains, strictly speaking, stationary; it does not grow into the wood, 
but the wood overgrows it. But what happens in the following season when a 
fresh annual ring is once more added to the wood? If the sinker had entirely 
ceased growing it would of necessity be ultimately completely closed by the layers 
of wood, as they develop with ever-increasing energy and add to the thickness of 
the branch, and at last it would be quite buried. To prevent this result, which 
would be fatal to the Mistletoe, a zone of cells is provided near the base of the 
sinker, which zone, at the time when the rampart of wood is being raised, adds in 
an equal degree to its own height, and causes, of course, an elongation of the sinker 
in a peripheral direction. The length of the piece thus intercalated in the haus- 
torium is exactly equal to the thickness of the corresponding annual ring in the 
surrounding wood of the branch. Thus at length the Mistletoe-sinker is found 
imbedded in a number of annual rings, although it has not grown into the latter, 
but has been banked up by them year by year. 
That zone of the sinker which possesses the capacity for growth, and which is 
always to be sought, in accordance with what has been said above, at the outside 
limit of the wood of the branch, in the so-called “bast” layer situated on the inner 
face of the cortex, produces, in the second year after the adhesion of the Mistletoe- 
embryo, lateral ramifications which are called cortical roots. They are thick, 
cylindrical, or somewhat compressed filaments, and all run close together under the 
cortex in the bast layer of the invaded branch. These rootlets issuing from the 
sinkers pursue a course parallel to the longitudinal axis of the branch, whilst the 
sinkers themselves are at right angles to the axis (see fig. 48°). If a rootlet springs 
from the sinker in a direction transverse to the longitudinal axis it bends imme- 
diately afterwards so as to be parallel to the long axis, and adopts the same 
direction as the rest, or else it bifurcates just above its place of origin into two 
branches which separate suddenly, and in their further course follow the axis of 
the branch. Thus it comes to pass that all the rootlets of a Mistletoe run up and 
down in the infested branch of the host-plant in the form of thick green parallel 
strands, but that none of them ever encircle the branch in the form of an annulaı 
coil. Each of these cortical roots may now develop from behind the growing-point 
new sinkers, which are formed in the same way as the first one above described as 
proceeding from the actual seedling. They, too, penetrate into the branch per- 
pendicularly to the axis, and as far as the solid wood are then encompassed by the 
growing mass of wood, but maintain the power of growth in the part close to their 
insertions, and in their growth keep pace with the thickening of the wood of the 
branch. The fact of the yearly recurrence of this formation of sinkers explains how 
it is that those situated nearest the growing-points of the cortical roots are the 
shortest, they being the youngest, whilst those which arise near the first sinker are 
the longest and oldest. It also accounts for the former being only inclosed by one 
annual ring of the host’s wood, and the others being surrounded by an increasing 
number of rings the nearer they are to the spot where the Mistletoe-plant first 
struck root. 
