Nov., 1922] KAUFFMAN AND KERBER HEART-ROT OF LOCUST 5OI 
contents, or a residue from wall surfaces. The forward movement of this 
zone of dark elements is, however, a significant consideration in interpreting 
this substance. It may not be out of place to speculate, from our advancing 
knowledge of colloidal chemistry, that, if it is of protoplasmic origin, 
colloidal stages might be assurtied of which the brown color is a character, to 
be followed by physico-chemical changes through which, by a change from 
the colloidal condition into molecular constituents, the color disappears. 
In such processes time is as much a factor as is the necessary ratio of the 
ingredients. Von Schrenk's (1914) findings in Syringa, according to which 
the brown substance is supposed to be destroyed by the fungus in its later 
activities, can play no part in our case. As will be shown later, there is 
no active mycelium behind the black zone to which we can refer this action. 
Nor can we say that the black zone is formed by the advance guard of the 
oncoming hyphae, since, as will also appear below, the hyphae are present 
and active beyond and outside the black zone. 
2. Lesser Rot Zone. Inside of the black zone, and by indefinable stages 
to the very rotten center, we have a zone marked sharply only on its ex- 
terior side. Here the decay may be said to be less complete than in the 
central zone. The hypha-holes through the walls of the elements were 
much larger and much more numerous than in the black zone. This was 
particularly true for the ray cells and the wood parenchyma. The cell 
contents of both ray and wood parenchyma had entirely disappeared. The 
larger hypha-holes were measured and found to range from three to ten 
microns in diameter. The other elements were all attacked by the hyphae, 
the holes being smaller and less numerous. The fibers seemed to be affected 
least of all. No hyphal threads could be found, although a diligent search 
was made for them. In a tangential or radial section containing the 
tracheids it is very easy to mistake the tertiary thickenings of the walls for 
mycelium, due to the width, color, and direction of these thickenings, and 
therefore scant attention was paid to the tracheids, the most careful search, 
however, being made in the wood parenchyma and medullary ray cells. 
When single macerated cells were teased out and examined, it was found 
that the holes made by the hyphae were rounded and smooth and much 
larger than the width of the hyphal threads as found later. This fact may 
be accounted for by assuming that the fungous enzyms still persisted 
although the hyphae had disappeared, and hence the diameter of the holes 
was increasing as solution continued. It was also found that in these 
isolated cells the hyphae must have entered the cells through the pits, as 
well as penetrating directly through the wall. The medullary ray cells 
and wood parenchyma, although badly decayed, did not break up in the 
same fashion that the vessels and tracheids did. The fibers held together 
very well. Not a particle of starch or even of living matter could be found 
in the wood parenchyma or in the ray cells of this portion of the decay. 
3. Badly Decayed Areas. In the center of the rotten core the wood was 
