4^6 AGRICUIvTURE OF MAINE. 



fined to killing outer portions of the bark on old limbs and the 

 killing back of the bark on younger limbs and twigs rather than 

 to the production of true cankers. On such branches the fruit- 

 ing pustules are found on the part which was first killed. The 

 dead bark is separated from the healthy bark by a sharp line 

 and is sunken as is shown in Kig. 78. The appearance of these 

 branches is very characteristic and they can be recognized by 

 one who has become somewhat familiar with the various can- 

 kers and twig blights, without microscopic examination of the 

 fungus. There is some reason to believe that the fungus is not 

 a very active parasite and it may be possible that such diseased 

 branches have been injuriously affected by some other agency 

 before the attack of this fungus.* 



Coryneum and Phoma cankers. In the examination of apple 

 cankers the spores of Coryneum foliicolmn and Phoma mali 

 have been found of quite frequent occurrence. Inoculation 

 experiments in 1909 proved that both of these fungi were capa- 

 ble of causing disease of healthy bark of apple branches. For 

 a detailed account of the study of these fungi the reader is 

 referred to Bulletin 170 of this Station. The appearance of 

 different stages of Coryneum cankers is shown in Figs. 79 

 and 80. 



Cytospora canker. A species of Cytospora has frequently 

 been found on small branches which have been killed back but 

 no true cankers have been seen. Those lesions observed have 

 much the same appearance as has been described for branches 

 on which Myxosporoium is found. After a little experience 

 one can distinguish the two fungi on the bark without the aid 

 of the microscope. 



In Bulletin 191 of the New York Station it is suggested that 

 a species of Cytospora found on diseased apple branches in that 

 State is probably parasitic. The Cytospora which occurs on 

 apple branches in Maine has been isolated, grown in pure cul- 

 ture where it fruits abundantly, and inoculations have been 

 made in small branches in the orchard. The fungus made only 



*The fungus has been isolated from such diseased branches and has 

 been grown in this laboratory upon sterilized apple wood and bean pods 

 for several months. Spores were produced in the cultures about one 

 month after the fungus was transferred from plates to bean pod 

 tubes. Some inoculations have been made and the results of these 

 will be given in a later publication. 



