DISEASES OF TAXODIUM AND LIBOCEDRUS. 33 
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 HCl. 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 
Pl. 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 
3 Bt 
