54 MISSOURI BOTANICAL GARDEN. 
rotted tissues the cell walls consisted only of cellulose, the 
lignin appearing in greater and greater quantity as the 
healthy wood was approached. This single instance alone 
seems to prove that the cellulose layer of the healthy wood 
does not have any connection with the cellulose left by the 
action of the fungus upon the cell wall. 
Still another instance was noted which seemed to con- 
firm and make this point doubly certain. Sections of 
trunks of trees of Populus tremuloides rotted by Fomes 
igniarius were examined carefully for the occurrence of 
cellulose. It was found that the wood fibers of the healthy 
wood in most cases had an inner, supernumerary layer 
which turned blue with chlor-iodide of zinc. The rotted 
tissues were separated from the healthy ones by a narrow 
infiltrated zone. Just inside this zone of infiltrated cells 
the affected fibers were of a very uniform thickness and 
the walls were decidedly thinner than those of the healthy 
wood where the cellulose was present. In the rotted tis- 
sues the cell cavities were also larger than in the unaffected 
cells. In other words the cellulose layer is more or less 
completely dissolved from the interior of the fibers, and 
the secondary layer is delignified, while the cellulose skel- 
eton is left until the last. 
These two instances seem to show that there can be no 
doubt regarding the solution of the supernumerary cellu- 
lose layer during the early stages of decay caused by some 
of the fungi. It is believed that this will prove to be true 
of most if not all of them. Hartig very evidently under- 
stood this and for this reason gave no further attention to 
the occurrence of cellulose as an extra layer in the wood 
fibers of oak wood than to mention its occurrence. * 
Actual measurements made in the wood fibers of the 
healthy and rotted wood of the same sections show beyond 
* Hartig. Die Zersetzungserscheinungen des Holzes der Nadelholz- 
baiume und der Kiche. 94, (1878). 
