20S MISTLETOES AND LOBANTHÜSES. 



sinker itself remains, sti-ictly speaking, stationary; it does nijt grow into the wood, 

 Ijut the wood ovei'grows 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 degi-ee 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 liaus- 

 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 brq.nch, 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 tlie form of an annular 

 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 witli the thickening of the wood of the 

 branch. The fact of the yearly recurrence of this formation of sinkera 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 I'oot. 



