DESCRIPTION OF PLATES. 



Plate I. (Frontispiece.) Sections of living white asli trees {Fraxinus americana) 

 attacked by PoJyporus fraxinophilus Pk. The upper figure shows an early stage; 

 the lower, a later stage of the decaying process. 



Plate II. Fig. 1.— Fruiting body of Polyporus fraxinophilus Pk. growing out 

 from a dead branch. This is a rather exceptional form of sporophore, which is 

 found only on branches. Fig. 2.— Two young sporophores of Pol t/jwr us fraxinophilus 

 Pk. growing on living ash. Fig. 3. — An old sporophore of Polyporus fraxinophilus 

 Pk. growing on living ash. 



Plate III. Fig. 1.— Transection of healthy ash wood, stained with iodine so as to 

 show the distribution of starch in the medullary ray cells and in the wood paren- 

 chyma surrounding the large ducts. This section is made just outside the dark line 

 dividing sound from diseased wood (see PI. I). Fig. 2.— Transection of diseased 

 ash wood, not stained, showing the distribution of a humus compound in the medul- 

 lary ray cells and in the wood parenchyma surrounding the large ducts. This sec- 

 tion is made just inside the dark line dividing sound from diseased wood (see PL I). 



Plate IV. 1.— Transection of ash wood, showing one form of change in the wood 

 cells caused by the fungus hyphpe. The darkly shaded parts are sound wood cells. 

 The white parts are wood parts which do not stain witli phloroglucin. (Magnifica- 

 tion same as for fig. 2.) 2.— Transection of medullary ray from the brown wood 

 layer, showing how the cells become filled with a brown humus compound, here 

 shown by the dotted areas. In two cells the dry compound has cracked. 3.— A 

 medullary ray, showing a later stage of fungus attack. The middle lamellte are dis- 

 solved out, separating the individual cells from one another. Note the absence of 

 the humus compound. (Magnification same as for fig. 2. ) 4 and 5.— Transection of 

 wood cells (highly magnified), showing various stages of change of wood into a 

 brown humus compound. Note the great thickness of walls of neighboring sound 

 cells. The humus compound is shown by the shaded parts. 6.— Starch grains from 

 medullary ray cell. Normal grains and several grains showing how grains are now 

 and then dissolved. The short line equals 10/i. 7.— Starch grains from diseased 

 wood, showing how the large grains are broken up into smaller ones. (Magnifica- 

 tion same as for fig. 6.) 8.— Transection from entirely rotted wood. The sound 

 wood cells at one side belong to a small piece of more resistant wood. (Magnifica- 

 tion game as for fig. 2. ) 



Plate V. Cross section of diseased trunk of the white ash kept in a moist place for 

 several weeks. The fungus hyphte have grown out from the diseased wood, forming 

 a white felt. 

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