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PLATE XXVIII. 
Fig. 1— Photomicrograph of a cross section of a portion of the sap- 
wood of a bitternut hickory (Hicoria minima) log rotted by Polyporus 
pargamenus, showing a black zone in transverse section, X 100. The 
wood at the right has been thoroughly decayed as the appearance of the 
cell walls will testify. At the left the wood is in the earlier stages of 
decay and is giving rise to decomposition products upon the advance of 
the decay. In the center is shown a black zone which separates the 
portions of wood in the different stages of decay. 
Fig. 2.— Photomicrograph of a radial section of a portion of the sap- 
wood illustrated in Plate XXVII, showing the formation of the brown 
drops of decomposition products in the pith-ray celis, X 100. The photo- 
graph was made of a portion of wood lying approximately one-half cm. 
within the external infiltrated portion. 
