30 DISEASES OF TREES 



advancing duramen. Even in the case of the silver fir and spruce 

 it is only the outer wood which conducts water, and in the bole 

 this region seldom embraces more than forty to fifty annual 

 rings, while in the branches it is much narrower. 



The damage done by the mistletoe to forest, fruit, park, 

 and avenue trees is by no means inconsiderable. In the 

 Reichswald, in the neighbourhood of Nuremberg, I have seen 

 woods of middle-aged Scotch pines where scarcely a tree had 

 escaped, and where the foliage of the mistletoes competed for 

 effect with the natural foliage of the pines. Where practicable, 

 as in orchards, &c., the infested branches should be entirely 

 removed before the mistletoe has had time to spread to any 

 considerable extent. Simply breaking off the plants only 

 induces the formation of vigorous root-shoots at the same 

 place. 



A few words may here be devoted to the genus Arceuthobium^ 

 of which a species, Arceuthobium Oxycedri, occurs in the south 

 of Europe, and also in Austria, where it forms dense bushes on 

 Juniperus Oxycedrus ; while in North America quite a number 

 of species attack forest trees, especially the Abietinece. These 

 grow in the same way as the European form, or induce the 

 formation of witches' brooms by the rhizoids which live in the 

 cortex causing considerable elongation of the infested branch, from 

 whose cortex numerous shoots I 2 cm. long break through at 

 irregular intervals, as happens in the case of Arceuthobium 

 Douglasii}- In the case of these plants, also, the nutritive sub- 

 stances are absorbed by simple sinkers consisting of a single row 

 of cells, or in other cases by vascular sinkers. The injury caused 

 to forest trees by these plants is very considerable ; still one 

 need not anticipate that these parasites will find their way into 

 Europe with the introduction of North American conifers. 



More interest attaches to Loranthus europceus, a parasite 

 specially common in Austria, but also found occasionally in 

 Saxony, the formation of whose roots differs entirely from that 

 of the Loranthacece already described. 



Loranthus europcziis is, for the most part, found on the 

 common oak, on which account it is known as oak mistletoe, 

 though it also attacks Castanea vesca ; and in Austria, especially 

 1 See C. v. Tubeuf, I.e. 



