AMERICAN CHESTNUT BLIGHT 695 



RESISTANT TREES 



The hopelessness of controHing the blight by any of the ordinary 

 methods naturally turned investigators' attention to a search for re- 

 sistant strains. Apparently there is some encouragement in this 

 direction, for early in 1008 Metcalfe pointed out that some strains at 

 least of the Japanese' chestnut are immune. Van Fleet^ reports from 

 twenty years' experience in breeding chestnut that: "The Asiatic 

 chestnuts, and the chinquapin-Asiatic hybrids, are plainly highly 

 resistant. Few have shown any appearance of infection and when 

 noticeable the injury is quite local in character. Second generation 

 seedlings of chinquapin-crenata crosses show no disease at all though 

 always exposed to infection." Morris^ (1914) reports that five trees 

 of C. molUssima have not been affected, although American trees have 

 died all around them. Specimens of C. alnifolia also have remained 

 free from the disease. In concluding on this point Anderson and 

 Rankin* state: "In brief, it may be said that there is no species of 

 Castanea which is wholly immune. Some varieties show marked re- 

 sistance, and Metcalf (1914) claims apparent immunity for certain 

 strains." The earlier work along this line seems to have dealt largely 

 with resistant foreign strains for orchard purposes. Later more 

 attention was given to forest conditions of the native chestnut. In 

 1918 A. H. Graves^ "investigated conditions in the American chestnut 

 looking toward immunity or disease resistance." He reports carrying 

 on a thorough search in the earliest infected regions (immediate vicinity 

 of New York City) and states that he found no immune trees but did 

 find a considerable number of resistant trees. He cites as evidence 

 of resistance the following: 



1. Reduction of average lateral growth of fungus in inoculation 

 tests. 



2. The occurrence of the trees in a neighborhood long subject to 

 the disease. 



3. Healed cankers, thrifty branches with bases diseased and hyper- 

 trophied but living, etc. 



4. Peculiarities of the bark ; such as extensive development of a 

 callus tissue, and the presence of a peculiar substance. 



5. The natural grouping of the trees in well-defined areas or 

 "pockets," pointing to a genetic variation. 



