Th a i 



MISTLETOE. 



413 



The plant sends down modified roots (haustoria), termed 

 sinkers, through the bark as far as the wood. It also emits lateral 

 shoots, or cortical roots, into the bast, chiefly in the longitudinal 

 direction of the branch of its host, and these do not grow down 

 into the wood. The growing 

 point of 'the cortical root ob- 

 tains nourishment from the 

 bast, but does not injure the 

 cambium ring ; the cortical root 

 sends down as far as the wood 

 fresh sinkers, which also absorb 

 nourishment: upward shoots 

 from it pierce the bark into 

 the air ; these, like the original 

 sub-aerial shoots, ramify and 

 become covered with foliage, 

 and bear fruit. The haus- 

 toria elongating outwards like 

 medullary rays become deeply 

 embedded in the wood of the 

 host by the growth of the 

 latter ; thus the older part of 

 the cortical root gets gradually 

 driven outwards by the growth 

 of the bast until it is cut 

 off by the formation of 

 corky tissue within the bast, 

 when it eventually falls off 

 with the older bark. The 



Fig. 200 (After Hartig). Diagram 

 representing the growth of the cortical 

 root and sinkers of mistletoe. The 

 terminal point of the cortical root (c] 

 is close to the wood. The growth of 

 bast (b) drives the cortical root nearer 

 and nearer to the outer hark, (e) are 

 dead sinkers, the cortical root of which 

 has been cut off for several years by the 

 production of cork in the bast. 



sinkers thus losing connection 



with the living mistletoe die 



inside the wood by which they 



are gradually surrounded. As 



they are formed of soft tissue, they soon decompose and 



eventually disappear, leaving a series of holes in the wood. 



This dying of the cortical root is quicker in the Scots pine 

 than in the silver-fir owing to the earlier formation of 

 rhytidome, or true bark, in the former. 



The portion of the host to which the 'mistletoe is attached 



