THE DECAYED WOOD. 23 



MICROSCOPIC EXAMINATION OF AFFECTED WOOD. 



Radial sections of the rotted wood reveal almost no places where 

 the mycelium has pierced the cell walls as is so common with other 

 wood-rotting fungi. Instead, the hyphaj pass through the pits, this 

 apparently being the rule. Cells and groups of cells, especially of 

 the medullary rays, are often found with masses of the mycelium in 

 their interior. The mycelium often forms an interwoven mass which 

 completely fills the cell lumen. • 



Cross sections of the pits can be gotten only in tangential niul 

 cross sections of the timber. The tangential sections show the cross 

 sections of the rays, and most of them have their component cell 

 walls, especially near the middle, wholly destroyed and the cavity 

 filled with mycelium matted closely together. The rotted wood is 

 so brittle that no free-hand cross sections can be made. 



The bordered pits have their closing membrane missing, and, as 

 already stated, the mycelial strands pass freely through them. Very 

 many ])its have their borders cracked, with one to several openings 

 running nearly to their periphery. The original opening of the pit is 

 often enlarged, although this is not generally very noticeable. wSec- 

 tions of the wood in the last stages of decay show that the middle 

 lamella is dissolved, thus allowing the cells to fall apart very easily. 



The cell walls undergo Some change wliich makes them exceedingly 

 brittle, the razor breaking rather than cutting them. No elasticity 

 is left in the tissues, the thickness of the razor being enough to cause 

 the sections to break into small fragments, wliich still stick slightly 

 together. The sections were cut free-hand, without embedding the 

 material. Numerous tabular crystals lie directly u])on the hyphse of 

 the fungus, which are apparently formed by the action of the fungus 

 on the wood. These crystals dissolve in hydrochloric acid without 

 effervescing. 



MICROCIIEMICAL TESTS OF AFFECTED WOOD. 



Phloroglucin and hydrochloric acid give a bright red in the rotted 

 tissues. Anilin sulphate and anilin chlorid give a bright yellow in 

 the affected wood. Delafield's hematoxylin gives blue throughout. 

 Chloriodid of zinc gives a blue color only in part of the tissues in 

 earh^ stages of the disease, but in later ones it gives blue tlu*ougliout. 

 Tliis bluing occurs in the early wood of the annual ring, shading off 

 as the late wood begins, then begins abruptly with the next annual 

 ring. Maule's potassium permanganate test gives a deep red in the 

 healthy wood, but none whatever in the rotted parts. Thallui sul- 

 phate gives a yellow in the rotted wood. Resorcin with suli)huric 

 acid gives a violet green not nearly so pronounced in the decayed 



214 



