72 PREVENTIVE AND COMBATIVE MEASURES. 



live for years on their host deriving nutriment from them ; 

 they also are detrimental to fruit trees because they bear 

 neither flower or fruit, and on some timber trees they so 

 deform the stems as to considerably reduce their value. The 

 witches' brooms of the cherry or the plum grow into large 

 infertile bushes of striking appearance, so that they may be 

 easily detected and removed in autumn or spring; those on 

 hornbeam, birch, and alder are of less practical importance, 

 but shoidd be cut off wherever accessible. 



Great damage is caused by the witches' broom (Aeddium 

 elatinum) of the silver fir in producing canker spots which 

 may in some cases attain gigantic dimensions and thereby 

 much reduce the value of the timber, or maybe render it quite 

 valueless. The cankered spots are, in addition, frequently attacked 

 by wound-parasites, whereby the stem is weakened and breaks 

 over at the canker, causing breaches in high forest, which can- 

 not be refilled. The witches' brooms should therefore, as far as 

 accessible, be cut off while still young, and all cankered trees 

 should be removed at the first thinning. 



The removal of twigs of plum bearing the so-called "pocket- 

 plums " or " fools " is also to be recommended, because the my- 

 celium of the fungi causing these hibernates in them. Eose-twigs 

 affected by rose-mildew {Sphaerothsca pannosa) should also be cut 

 away as soon as possible, before many plants have fallen victims. 

 Portions thus removed are both worthless and dangerous, hence 

 should be destroyed. So also all trees rotted by fungi should 

 be removed from their healthy neighbours, and, if possible, 

 burnt or buried, or otherwise rendered harmless. 



This forms a convenient place to consider generally the 

 wood-destroying wound-parasites of our timber-producing 

 plants. 



The wood-destroying wound-parasites belong chiefly to the 

 families of the Polyporeae and Agaricini, and each possesses a 

 mode of life and method of destroying its host, so similar to 

 that of its relatives, that it is quite impossible to consider them 

 separately in a practical way. They are enemies of our fruit 

 orchards, our parks, and our forests, and the means to be em- 

 ployed against them varies in the hands of the fruit-grower, the 

 gardener, or the forester. 



Every fruit-tree, whether grown in a garden, an orchard, or 



