Undescribed Timber Decay of Pitch Pine 267 



sound wood of Pinus rigida the vertical tracheids give the reac- 

 tion for lignin with the exception of the inner surface of the 

 bordered pits. These remain practically uncolored in the center 

 but most of them show a narrow ring of red at the outer margin. 

 In sections showing the structure of the tracheid walls the middle 

 lamella, secondary lamella, and tertiary or inner lamella all give 

 a lignin reaction that varies in intensity in the different parts. 

 Consequently there is little free cellulose in the vertical tracheids. 

 The medullary rays of the sound wood of pitch pine are bordered 

 above and below with one or more series of horizontal ray 

 tracheids with inner walls conspicuously denticulate as is char- 

 acteristic of the pitch pine group. These give a definite lignin 

 reaction and do not respond to the cellulose test. The ray pa- 

 renchyma cells, on the other hand, soon develop the characteristic 

 lavender-violet color when treated with chlor-iodide-zinc solu- 

 tion. Consequently they are. composed of unmodified cellulose. 

 These reactions of the sound wood serve as a basis of compari- 

 son for detecting changes in the wood decayed by the fungus. 



When the wood becomes infected with the mycelium of the 

 fungus the medullary rays are first attacked. The ray paren- 

 chyma cells disappear rapidly as can be readily seen either in 

 tangential or radial sections of the wood. The cells that still 

 persist in the angles of the rays as seen in tangential section are 

 ray tracheid cells. Their lignified nature enables them to with- 

 stand the attacks of the mycelium for a somewhat longer time. 

 Undoubtedly the rot progresses rapidly inward along the line 

 of the medullary rays. In radial section these hyphae can 

 readily be traced within the cavity formerly occupied by the ray 

 cells and are seen to send off frequent branches into and between 

 the vertical tracheids of the spring wood. The intercellular 

 hyphae enter the tracheids either through the bordered pits or 

 apparently by simply dissolving a hole through the wall, as many 

 such irregular holes can be seen and how they could otherwise 

 originate is not plain. As the hyphae pass through the bor- 

 dered pits these rapidly become disorganized and many different 



cellulose is present it becomes a bluish-lavender color in this solution. 

 Usually the reaction is slow in appearing and increases to a maximum in- 

 tensity in a very few minutes. The sulphuric acid-iodine test was also used 

 but found much less satisfactory. 



