72 PROTECTION OF WOODLANDS. 



woodlands : the horticulturist tries to exterminate it by an early 

 clearance of the easily visible growth from his fruit trees. 



Tlic Oak Mistletoe (Loranthus europceus\ injurious to Oaks and 

 Sweet Chestnut, and of especially frequent occurrence in Central 

 Austria, affects trees in a similar manner by producing excrescences, 

 often the size of a man's head, above which the stem or branch 

 sickens, and even dies off. Preventive measures for obviating 

 danger from this parasite are also wanting. It is not found in 

 Britain. 



It may here be mentioned in passing that Lichens are not 

 parasites, but are merely to be considered a sign of damp air and 

 want of energy of tree-growth. With the very gradual thicken- 

 ing of the girth of the tree, and the slow peeling off of the bark 

 scales, the lichens have points of contact and places of abode 

 offered to them which would be wanting if the bark were smooth. 

 By stopping up the numerous lenticelles or air-holes of the bark, 

 through which the tree takes up oxygen in summer, direct 

 injurious consequences to the tree can however follow, and the 

 dying off of branches inside the crown, that are thickly covered 

 with lichens, may frequently be noted. 1 The horticulturist 

 therefore removes lichenous growth ; but this can hardly be carried 

 out in Sylviculture. 



Ivy (Hedera helix) is also no parasite, for it derives all its 

 nourishment from the soil, and all the rootlets appearing on 

 stems and branches are merely supporting rootlets. 



41. Fungi : their Evil Effects, and the Preventive Measures 

 adaptable against them. 



Not a small proportion of the disturbances that take place 

 in the growth of plants, from minor injuries quickly healed n^um 

 up to such as lead to the death of the plant or tree, is occasioned 

 by parasitic, cryptogamous vegetable organisms, fungi t living in or 

 on the plants in questions. 



Until the last few decades, this pathological branch of phyto- 

 logy had received extremely little attention, so far as concerned 

 the fungi parasitic on forest trees ; many of these were totally 



1 In the Ccniralblatt fiir das gcsammte Forslwesen for 1889, page 275, a case 

 detailed in which the woodlands, in a damp mountain valley, with a crop of Spnir< 

 Larch, and Scots Pine, suffered to such an extent from being overgrown with eigl 

 apcies of lichens, that about 60 per cent, of the trees were dying prematurely. 



