Issued June 80, 1911. 
U.S. DEPARTMENT OF AGRICULTURE, 
FOREST SERVICE—BULLETIN 92, 
HENRY S. GRAVES, Forester. 
LIGHT IN RELATION TO TREE GROWTH. 
BY 
RAPHAEL ZON, 
CHIEF OF SILVICS, 
AND 
HENRY S. GRAVES, 
FORESTER. 
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WASHINGTON : 
GOVERNMENT PRINTING OFFICE 
1911, 
