3/6 MAINE AGRICULTURAL EXPERIMENT STATION. I9IO. 



from the galls of peach, hard galls of apple, hairy root of apple, 

 hops, rose, and chestnut, which were found to be very similar 

 if not identical with the organism from the daisy. 



The fact that crown gall of the apple is now definitely known 

 to be caused by a parasite which also causes galls of a number 

 of other plants is of great importance in the control of the dis- 

 ease. It will be readily seen that young apple trees should not 

 be set in land on which another plant affected with this disease 

 has been grown. 



In the apple, the greatest amount of infection is likely to take 

 place in nursery stock, as the trees are grown rather closely in 

 the nursery row. When affected trees are set in the orchard, 

 new galls develop from year to year and in many cases the trees 

 weaken and die. Little good is accomplished by cutting off the 

 galls at the time of setting the trees, as it is practically impos- 

 sible to remove all of the infected tissue and new galls develop. 

 It is best to secure apple trees from nurseries which are free 

 from the disease, but in case diseased trees are received they 

 should be destroyed. In the cultivation of orchards in which 

 trees affected with this disease are known to occur, care should 

 be taken that healthy trees do not become infected through in- 

 juries near the surface of the ground. 



Wood destroying fungi. It is a well known fact that the 

 heart wood of apple trees is often decayed. In many cases the 

 extent to which the wood has been destroyed is not realized by 

 the owner of a tree until it is blown over by a heavy wind and 

 it is found that only a thin shell of sap wood remains. Such a 

 condition is shown in Fig. 265. 



It is not so generally understood by orchardists that this decay 

 is caused by the growth of fungi. In some cases the mycelium 

 of a fungus may grow on the interior of a tree for years before 

 there is much evidence of its growth on the outside. Then after 

 the mycelium has stored up a sufificient amount of food, the 

 fungus produces its fruit. In many cases these wood destroy- 

 ers belong to the bracket or shelf fungi of which a number of 

 species have been reported on the apple. Ver}'- frequently the 

 wood of apple trees is badly decayed before the fungus fruits 

 and then it is too late to apply a remedy to the tree. 



Wood destroying fungi enter the wood of trees through 

 ■ wounds which may be caused in various ways. Some of the 



