26 DISEASES OF TREES 



Japan. It is met with on almost all dicotyledons and conifers, 

 but exibits a preference for certain species, e.g. silver fir, Scotch 

 pine, poplars, and fruit-trees ; whereas on others, e.g. spruce, oak, 

 beech, Spanish chestnut, alder, and ash, it has been met with 

 either very seldom or not at all. 1 With regard to the appearance 

 of this familiar plant, it need only be mentioned that narrow and 

 broad-leaved varieties occur on different species of trees. The 

 mistletoe is distributed by thrushes (especially Turdus viscivorus], 

 which feed upon the berries and carry them off. The birds dis- 

 engage the sticky seeds from their beaks by rubbing them against 

 the branches on which they perch, and to which the seeds there- 

 by become attached. The seeds, which germinate in spring, first 

 of all develop a kind of sucker, from whose centre a fine root 

 appears which pierces the tissues of the cortex. This main root 

 penetrates to the wood of the branch or stem, which, however, 

 it is too delicate to enter. This then finishes its apical growth 

 in length, but, on the other hand, owing to the presence of 

 meristematic tissue behind the apex (such tissue being situated 

 in the region of the cambium of the host-plant), it is enabled to 

 elongate at the same rate as the branch increases in thickness, 

 by the formation of a ring of wood and of bast (" intermediary 

 growth in length "). Owing to the fact that the wood-ring en- 

 velops the apex of the root of the mistletoe, the latter appears 

 to bore deeper into the wood each year, but this is really due to 

 its being embraced by the stem as it grows in thickness. The 

 growth in length of this root, as of all the " sinkers " that after- 

 wards originate in the roots that are met with in the cortex, 

 very closely resembles the growth in length of a medullary ray 

 possessing cambium of its own in the cambium mantle that 

 covers the whole stem, and is thus enabled annually to elongate 

 both towards the wood and towards the bast. Several lateral roots 

 next appear on that part of the radicle which is situated in the 

 cortex, and these proceed to grow both upwards and downwards 

 in the branch. These " Rhizoids " or " Cortex-roots" push their 

 pencil-like apices along the young soft bast, without however 

 coming into contact with or altering the cambium zone. The 

 organs of the soft bast are dissolved in front of the point, and it 



1 Nobbe, " Ueber die Mistel, ihre Verbreitung, Standorte, und forstliche 

 Bedeutung" Thoranderforstlichesjahrbuch, 1884. 



