Necrosis of the Grape Vine. 



339 



does not recognize a diseased vine (this is evidenced by the fact that 

 many vines are trimmed and tied up and still fail to put out shoots), 

 he goes from diseased to healthy vines and often carries a very small 

 sliver of diseased wood on his shears or saw, which is deposited in the 

 healthy vine. It would be exceptional and purely accidental if he should 

 infect every arm of a vine at a single trimming. 



It is not an uncommon sight to see vines injured near the base from 

 bruises by the various implements. In this way, also, diseased tissue 



Photo. Oct. 26, 1908 

 Fig. 55. — Niagara. Cross sections of diseased stems {natural size) 



might be carried along and forcibly injected into healthy vines. Until 

 infections were found on the green shoots these two methods were 

 thought to be commonest and perhaps the only means of infection. The 

 idea that it is a common method is supported by several facts. The 

 action of the fungus on the old hardwood of the vine is very slow and 

 the progress made is much like that of a wound parasite. This term 

 is one which is frequently used in reference to heart diseases of trees. 



