502 
AMERICAN JOURNAL OF BOTANY 
[Vol. 9! 
SO brittle that good free-hand sections could be made only with great 
difficulty. An attempt to imbed and make microtome sections failed 
because of the crumbly nature of this material. It was noticed that the 
size of the hypha-holes had increased, until in places the walls were so 
thoroughly riddled that they had parted as soon as the middle lamellae 
were dissolved by the maceration fluid. All the elements were so affected, 
with the possible exception of the fibers which still held the wood together, 
supported by the skeleton cell walls of the rays. The tracheids and vessels 
were merely a broken mass of fragments and recognizable only through 
their spiral markings, etc. In both the medullary ray cells and the wood 
parenchyma, it appears that the hyphae merely utilized the starch and 
other contents of these cells and then worked through from these cells as 
origins, to the vessels, tracheids, and fibers. The wood parenchyma 
surrounds the vessels in Robinia, and therefore this would be a particularly 
good place for the hyphae to work from. This is also true of the ray cells, 
which are very closely linked up with the other elements. 
In macerated portions of this badly rotted area, it was found that the 
wood parenchyma and the medullary ray cells, although badly riddled, 
still retained their original outlines and were still easily recognizable, 
whereas the tracheids and vessels were recognized only through the frag- 
ments that had spiral markings. The fibers in most cases were perforated 
in scattered areas but still held together strongly. 
The very end decay showed nothing but the fibers remaining, and these 
of a distinctly colorless appearance. The wood parenchyma and medullary 
ray cells were now not very easily recognized. These fibers were very 
uneven in outline, indicating that most of the wall had been dissolved 
away. It is these fibers that give the appearance of white mycelial patches 
in the very end decay, when the decayed material is placed in water for 
a few days. 
4. Apparently Sound Wood outside the Black Zone. Having failed in 
all our studies to locate mycelium in the rotten portion of the trunk, an 
examination of the apparently sound wood was undertaken. For this 
purpose a slab was selected which still had three inches of sound wood out- 
side the black zone, viz., section VII. This was supplemented by section I, 
with a narrower border of sound wood. Free-hand slices were at first 
made about two millimeters outside the black zone, and here mycelium 
was found in abundance. The mycelium was exceedingly fine, from i to 
1.5 microns in diameter, hyaline, and could easily be confused with edges 
of walls, etc., except for its characteristic windings and branchings and for 
the presence of delicate cross walls. Under the eosin stain it assumed a pale 
greenish color which contrasted sufficiently well with the reddened color 
of the cell walls to double our assurance. When it occurred in the wood 
parenchyma as seen in tangential sections, the threads were usually parallel 
to the long axis of the cell and had branches which penetrated the adjoining 
