342 Keport of the Horticultui{ist of the 



bark, but those spores that chance to fall and germinate in a 

 wound, produce the cankers. Other spores are deposited on limbs 

 that have an abundance of dead and decaying outer bark where 

 they find conditions suitable for growth. In such instances no 

 direct injury is done to the tree, but spores are produced and dis- 

 seminated so that a constant source of infection is maintained. 

 The spores possess great vitality since some of them germinate 

 after having been kept a year in the laboratory. 



In some instances the mycelium apparently lives over winter 

 and continues its growth the following spring. The formation of 

 the largest cankers can scarcely be explained in any other way. 

 However, in all of the inoculations made in the spring of 1898, in 

 only one instance did the resulting canker enlarge any^ during 

 the present season. See Plate XXX, fig. 3. 



does the mycelium penetrate the wood ? 



This question is suggested by the presence of two or more 

 cankers on the same limb, the external appearance of the more 

 recent ones suggesting the jaossibility of the fungus having passed 

 from the old canker through the wood and appearing on the sur- 

 face of the limb at favorable points where the newer cankers 

 were formed. An examination of a number of specimens and the 

 occurrence of pycnidia on decorticated wood shows that while the 

 mycelium does penetrate the wood to some extent, the fact is of 

 little economic importance. One limb was examined that had 

 five small cankers on it at intervals of about a foot. On split- 

 ting the limb it was found that the mycelium had penetrated the 

 wood at but one point and that for only a short distance. 



PREVENTIVE MEASURES. 



Although experiments in treating this disease are under way no 

 results have yet been reached and from the nature of the fungus 

 it will be seen that a number of years must elapse before data 



