370 MAINE AGRICULTURAL EXPERIMENT STATION. IQIO. 



killed trees in this State. In the case of young trees the fungus 

 may in some cases girdle the tree in a few weeks and thereby 

 cause its death. The same holds true of small branches of old 

 trees, but in the case of large branches the fungus usually spreads 

 but a few inches each year forming true cankers, and the rough, 

 blackened areas that are frequently seen on large branches often 

 represent a development of several years. The living tissues 

 attempt to heal over the wound by the formation of callus and 

 in some cases with considerable success. Often the parasite 

 ceases to spread in the bark when the dry season of summer 

 comes on and a crack forms between the healthy and diseased 

 bark. The following year the diseased area may continue to 

 spread or the callus may check it considerably. Often other 

 fungi, some of them saprophytes, grow upon the dead bark. 

 Thus it may be seen that while fungi which enter through win- 

 ter injuries may spread and ultimately do great damage to the 

 tree,' there is no reason to believe that the death of large trees 

 which was observed in Maine orchards immediately following 

 the winter of 1906-7 was due to a parasitic organism because the 

 trees died in many cases in too short a time for their death to 

 have been caused by such organisms. On the other hand, there 

 were many places injured by that winter, which became infected 

 by fungi. Where these have been neglected the diseased areas 

 have spread from year to year and have done much damage, 

 often developing into true cankers. 



There are many other wounds than those caused by freezing 

 through which parasitic fungi may enter. By this it is not meant 

 that every wound that is made in the bark will necessarily be- 

 come infected and develop into a diseased area. Frequently 

 small wounds in the bark of young branches heal over quickly, 

 without infection and no serious damage is done. In many 

 cases, however, the spores of parasitic fungi are carried to 

 wounds. This is especially liable to be the case when diseased 

 branches are allowed to remain on the trees, or old neglected 

 trees in the neighborhood produce abundant crops of fungus 

 spores from year to year. Some of the ways in which wounds 

 are made are : Barking of trunk and branches by machinery 

 in cultivating and caring for the orchard ; injuries by ladders and 

 by men in picking fruit; branches are sometimes injured by 

 props used to support a heavy load of fruit especially when they 



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