315 



suckers, which come into contact, like the original root, with the surtace of the 

 wood." " The wood and bark of the mother plant, in their periodical increase, 

 form layers aroxmd the suckers, which grow in exactly the same manner in the 

 cambial stratum " (Pitra) and thus the hardened suckers come to be imbedded 

 in the body of the wood. Dr. Harley goes on to state, amongst many other 

 mteresting particulars relating to the growth of the plant, that their perpen- 

 dicular roots are tapering, diminishing in size from the circumference towards the 

 centre ; that there are usually three or four and sometimes five or six such 

 perpendicular roots ; that their terminations are always composed of delicate 

 tubular cells joined end to end, and arranged parallel to each other and to the 

 long axis of the root, and that these roots are always arranged strictly parallel to 

 the medullary rays of the nourishing plant. " The young cellular root of viscum 

 may be regarded generally as a prolongation of the central pith of the parasite, 

 and contiguous medullary rays of the nourishing plant are successively confluent 

 with its surface."' 



Having minutely described the loose porous structure of the stem and base 

 of the Mistletoe, Dr. Harley says " with regard to the direction and arrange- 

 ment of the roots of the Viscum which'lie within the wood, this is determined by 

 the arrangement of the medullary system of the nourishing plant, the roots always 

 lying strictly parallel to the medullary rays ; " a conclusion to which he was led 

 by the fact that the Mistletoe and the supporting branch grow at right angles to 

 each other, and that on a transverse section the Mistletoe roots are always shown 

 to be arranged like the radii of a circle from the circumference towards the central 

 pith. 



" The horizontal ramifications (side roots) of the base of the Mistletoe have 

 plainly the same structure as the j-oung perpendicular roots. Whichever direc- 

 tion they take, they produce at frequent and pretty regular intervals, other taper- 

 ing cellular roots which, guided doubtless by the medullary rays of the bark, 

 press towards the surface of the wood and are thus brought in contact with the 

 ends of its medullary rays. They are subsequently found embedded at various 

 depths in the hard wood of the nourishing plant, like the primary roots. These 

 lateral roots also give origin to budlike processes, which, deepening in colour, 

 grow up obliquely through the bark, and appear as little shoots in the chinks, 

 soon developing leaves and stems as a ' sepsurate plant.' — Dr. Harley also gives 

 gives good ground for believkig the perpendicular roots penetrate the hard wood 

 by their own growth, in thL absorption they occasion in the wood itself, and in the 

 depth to which they enter — a conclusion which all who have made careful sections 

 of the bough with the Mistletoe attached to it, will have no difficulty in believing. 

 It forms another example cf the common law in organic life, that when two living 

 structures impinge on each other in a confined space, the one possessing the 

 lowest power of vitality must give way to the other, and here it is the dense wood 

 of the tree that is gradually caused to be absorbed by the pressure of the soft 

 cellular growth of the perpendicular roots of the Mistletoe. 



" When the roots of the Viscum album," says Dr. Harley again, " have be- 

 come fairly infixed into the medullary system of the nourishing plant, their outer 



