IQO 



PLANT DISEASES 



curved; flesh very thick, soft, pure white; pores on the 

 under surface very minute, white. Varying in size from 

 three to eight inches across. 



When the fungus first attacks the hving wood it pro- 



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Fig. 43. — Polypoms betulinus. Fungus about Oiie-quarter 

 nat. size; section of same. 



duces a brown discoloration, due to a ferment present m 

 the mycehum ; by means of this substance the thickening 

 layers of the cell-walls are dissolved and absorbed, the 

 middle lamellae of the cells alone remaining. Finally 

 cracks are formed in the soft, decayed wood, containing 



