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BENT F. S0EGAARD 



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ac 60j j 



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I YEARS I YEARS £ 



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12345 12345 



INFECTION CLASS 



12 3 4 5 



Figure 3. Degrees of infection of hybrid seedlings of Pinus 

 strobus x Pinus peuoe at various ages by Cronartium vibicola: 

 seed collection S. 873-45. Infection classes: l--healthy (net 

 infected), 2--healthy (previous infections were defeated), 3-- 

 branch infection only, 4--stem infections, 5--dead. 



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 601 



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 20 



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17 

 YEARS 



JJiLl 



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12345 12345 



INFECTION CLASS 



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Figure 4. Degrees of infection of open pollinated seedlings of 

 a hybrid between Pinus peuoe x Pinus strobus at various ages by 

 Cronartium ribicola: Infection classes: l--healthy (not infected) 

 2--healthy (previous infections were defeated) , 3--branch infec- 

 tion only; 4--stem infections, 5--dead. 



