STATE POMOLOGICAL SOCIETY. 85 



called canker. In this work it has been necessary to isolate 

 fungi in pure culture and then to inoculate trees in such a man- 

 ner and in such number as to insure that the interpretation of 

 the results was correct. 



There can be no question that much of what the orchardists 

 of Maine are now calling canker had its origin in winter killing. 

 The fungi which cause disease of the bark and wood are very 

 rarely able to enter through uninjured bark. The bark killed 

 by cold gives just as good an opportunity for a fungus to enter 

 as a wound made in any other way. But whatever the origin of 

 the trouble may have been, it is necessary to try to check the 

 spread of that part of it which is caused by parasitic fungi. This 

 may be done to a considerable extent by removing and burning ■ 

 dead branches on which the fungi occur. In the case of 

 branches which show injured regions much may be done by 

 carefully removing the dead bark and the part of the wood which 

 is injured, disinfecting thoroughly with copper sulphate solu- 

 tion, and then painting over with white lead in oil. The main 

 thing to keep in mind is the destruction of the living fungous 

 material which is capable of spreading infection wherever 

 wounds occur. It is not enough that the diseased branches be 

 removed from the tree. They mnst be burned to destroy the 

 fungus because in many cases fungi are able to grozv and pro- 

 duce millions of spores on zuood zvhich has been removed from 

 the tree. When the orchardist realizes that the fungi which 

 cause the diseases of his trees are living plants which are able 

 to grow and reproduce he is better able to understand the rea- 

 sons for taking certain measures to prevent the spread of fun- 

 gous diseases. 



So far in our work we have found that what is usually called 

 canker of apple branches in Maine is due to only two general 

 causes. One is injuries due to weather conditions of which 

 winter-killing is the main one, the other is attacks of parasitic 

 fungi of which there are at least 4 in the State which are known 

 to do considerable damage and there may be others. We have 

 not found any case in which we considered that canker was 

 caused by the organism which causes fire blight of the pear. 

 It is well known that this organism causes disease of apple trees 

 but we have not found it in Maine either on pears or apples, 



