500 
AMERICAN JOURNAL OF BOTANY 
[Vol. 9, 
simple pits where they communicate with the wood parenchyma, and semi- 
bordered pits where they communicate with the vascular tissues, such as 
the tracheids and vessels. 
Diseased Wood 
Both macerated material and free-hand sections of the different stages 
of the rot were used. By this means data were obtained as to the exact 
role played by each kind of element in the advancement or retardation of 
the mycelium in the wood. For maceration, the pieces were placed in a 
solution containing lo percent nitric acid and lo percent chromic acid in 
equal proportions. The containers were kept in a warm bath for 2^ hours, 
then washed clear of the acid and kept in water with a few drops of chloro- 
form. The free-hand sections were stained with eosin in order to bring 
out the hyphae when present. The following results were brought out by 
these studies: 
I. Black Border or Transition Zone. Here was noticed a distinct, 
narrow, dark-brown strip of rot, whose elements were infiltrated for the 
most part by a brownish substance. This circular strip was varied by 
small, V-shaped irregularities, the point of the V taking its origin in the 
medullary ray and wood-parenchyma cells. These two kinds of elements 
also contained the darkest infiltrations, especially the ray cells as observed 
in tangential section. The base of the V-shaped irregularities encompassed 
the tracheids, vessels, and both kinds of wood fibers. The contents of the 
last named were much lighter in color, and seemed to indicate greater 
resistance on the part of these elements to the dissolving action of the 
hyphae. No hyphae were observed in this zone, but evidence of their 
former presence was plentiful; the ray cells and wood parenchyma showed 
the characteristic small, rounded perforations, and some of the pits of the 
tracheids and vessels were eroded. All kinds of solvents and stains were 
tried to change the color of the brown deposit, but without success. In 
general it may be said that little damage seemed to have been caused by the 
hyphae, for the elements seemed perfectly normal except for the brown and 
blackish inclusions and the holes made by the hyphae in the walls. This 
zone, as far as its woody elements are concerned, is in about the same stage 
of decay as the apparently sound zone beyond it, which is to be discussed 
later. If hyphae were present, they must have been overlooked because of 
the optical difficulties in the study of this zone. 
This blackish-brown substance has been variously accounted for. 
Rhoads (19 17) gives a summary of the views held by different workers. 
That it is a phase in a series of chemical changes taking place within the 
dead cells seems an unavoidable conclusion, since the zone containing these 
colored inclusions passes outward as the rotten core advances radially. 
We d d not concern ourselves with the question of its origin, whether an 
infiltration, a gradual change from original protoplasm and other cell 
