DISEASES OF TAXODIUM AND LIBOCEDRUS. 



acteristic, and in preparations of much-decayed wood large 

 numbers of the circular discs can be seen floating about. 



The micro-chemical reactions are marked. Any investi- 

 gation into the chemical nature of wood substance is apt to 

 be rather unsatisfactory. It is possible to record certain 

 well-marked reactions, but often their true significance will 

 not be apparent, because our knowledge of the complex 

 constituents of wood, and particularly of its decomposition 

 products, is still so very meager. 



The most characteristic reaction is the one with phloro- 

 glucin and HC1. If a section, preferably a transection 

 of wood cut so as to include the outer portion of the 

 decayed area, and some of the surrounding wood, be treated 

 with this reagent, an appearance such as is represented on 

 PI. 3, fig. 1, is obtained. The cells of the sound wood 

 i. e., wood in which no recognizable morphological 

 change has taken place, stain dark red purple. The pri- 

 mary lamella stains much deeper (p). Passing to cells 

 further inward (towards the diseased spot) the tertiary 

 lamellae of some cells no longer stain red purple but yellow 

 (d). This yellow coloration increases as one passes on, the 

 red decreasing correspondingly, until at a certain stage 

 only the primary lamella is stained red. The pits are the 

 first areas to show the yellow color. On a radial longitu- 

 dinal section the contrast between the surrounding wall and 

 the pit is very marked, the latter looking like a hole in a red 

 field. In the final stage the remaining parts are entirely 

 yellow, no red being visible. The yellow coloration appears 

 first along the medullary rays, and is always in advance of 

 the same reaction in the intervening wood cells. Hand in 

 hand with the disappearance of the red color goes the 

 shrinkage of the secondary lamella, as described. This 

 reaction of the cell-wall is due to the gradual extraction of 

 the coniferin elements of the walls. They are at first 

 extracted from the innermost lamella, then from the 

 secondary lamella, and last of all from the primary 



11 



