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BOOKS AND CURRENT LITERATURE 



closure of substomatal cavities and intercellular spaces, the result of hy- 

 pertrophic changes in the spongy tissue. This retardation of transpira- 

 tion in apple leaves is believed to be a factor in accounting for the bad 

 physiological condition of affected trees. This would not appear to me, 

 however, to be as potent a disturbing factor as the reduction in the 

 photosynthetic area due to the presence of the numerous aecial sori, — 

 Frederick A. Wolf. 



