1902.] KATUKAL SCIE>'CES OF nilLADELPinA. 491 



lar wedge-shaped masses of a rich browu color, consisting of the 

 bvokeu-dowu cells, a mass of hyphoe and a yellowish-brown matrix 

 formed as a waste product by the host cells that are attacked l)y 

 the fungal parasite. These masses of dead tissue jn-oceed radiately 

 outward. Their inner side is more or less evenly rounded and 

 conforms to the general concentric arrangement of the annual 

 rings (fig. 31). Their outer edge is more or less irregular, as the 

 disease progresses by proceeding outward along the wedges of wood 

 between the medullary rays (fig. 31). These diseased areas may 

 become more or less confluent as the pathological tissue increases in 

 amount by the spread of the fungus antagonistic to the host (fig, 

 31). AVhere these wedge-shaped browu areas touch the cortex the 

 cortical cells become involved, assuming a darker, richer browu color 

 with the death of the cells attacked. As these browu patches 

 increase in size, the hyphie which have grown out into them keep 

 pace with the dissolution of the healthy tissues, until, as before 

 mentioned, they form a complex of considerable extent. 



The breaking down of the tracheids begins much in the same 

 manner as in the disease of the white cedar induced by G. bisej)- 

 tatum, but the final result is different. The same springing loose 

 of a part of the lignified cell wall is observable (fig. 32). When 

 two adjacent tracheids have been thus affected, the middle lamella 

 is dissolved away and a cavity, two tracheids in diameter, is 

 formed. If three or four adjoining tracheids are involved, the 

 space becomes larger (fig. 33). These spaces are filled with a 

 brown residual material, and by the confluence of a number of 

 smaller bi-owu diseased areas the wedged-shaped diseased spots are 

 formed, which later become fissui'ed by the appearance of crack-like 

 intercellular spaces. In older stems, the appearance of the diseased 

 brown areas and the increase in width of the annual wood-rings 

 seem to be correlated. The fifth and sixth annual rings in a stem 

 eleven years old seem to be most involved, and here, with the excep- 

 tion of one small unaffected patch of tissue, the brown tissue forms 

 a continuous band of variable thickness and pathological appear- 

 ance about the stem. The spring wood of the sixth year here 

 seems to be most involved. From this ring arms of diseased wood 

 radiate out through the seventh, eighth, ninth, and on one side of 

 the stem to tiie cortex through the eleventh and last annual Hug of 

 wood. An enumeration of the number of tracheids in a radial row 



