552 
Journal of Agricultural Research 
Yol. XXIX, No. It 
data.) Table IV shows that large holes 
are more commonly found in the brown 
rots than in the white rots (with a nota¬ 
ble exception in Polyporus schweinitzii ). 
The white pocket rots so far studied, as 
a rule show small bore holes and con¬ 
stricted hyphae. Spiral shrinkage 
cracks appear to be exclusive features 
of the brown rots and apparently the 
enzymes of the causal fungi have here 
played an important part. The fact 
that brown rot fungi can apparently 
remove from the cell wall much of the 
so-called cellulose complex, leaving 
most of the lignin compound (see under 
“Decay processes ’’ above), may be a 
clue to the origin of these cracks. May 
not the cracks, forming at the weakest 
tension point, follow the hollows be¬ 
tween the spiral thickenings laid down 
in the formation of the tracheid cell 
wall? Another question is suggested: 
Do shrinkage cracks appear only in the 
wood tissues infected by fungi or are 
they found in sound tissues as well? 
Upon this answer hinges the diagnostic 
value of shrinkage cracks in wood tis¬ 
sues where hyphae are not observed. 
It is not inconceivable that the enzymes 
of a wood-rotting fungus may affect the 
tissues ahead of the hyphae and so pro¬ 
duce shrinkage cracks in tissues where 
hyphae are lacking(f£, 26,35,51, p. 379). 
As an example of the value of micro¬ 
scopical characters in decay diagnosis, 
the differences between Trametes pini 
and Polyporus circinatus may be cited. 
The hyphae of Trametes pini in Picea 
canadensis are constricted in passing 
through the comparatively small bore 
holes in the cell walls and are commonly 
seen to penetrate in a direct line across 
the section through many walls. 
Buckles are observed. The hyphae of 
Polyporus circinatus in Picea mariana 
are not constricted, and the bore holes 
are usually much larger than the hy¬ 
phae passing through them. The ma¬ 
jority of the hyphae run lengthwise of 
the long axis of the cell. Only a few 
penetrate many cell walls in a direct 
line, and none show buckles. 
Again, in the incipient stage of Echi- 
nodontium tinctorium in Tsuga hetero- 
phylla bore holes and hyphae are numer¬ 
ous and the surfaces of the cell wall; 
appear slightly pitted or corroded. Th 
hyphae penetrate the tracheid cell wall 
and pass through the bordered pits, in 
places filling the cell cavities with 
masses of branched and twisted hypha . 
The hyphae have a tendency to concen 
trate in the medullary ray cells. N 
great changes are noted in the cell walls 
In the typical stage there is a marked 
dissolution of the cell walls, particu¬ 
larly in the region of the ray cells (fig. 
5, Cd.). The decrease in width of the 
cell walls is marked, the fungus attack¬ 
ing the tertiary wall first, the dissolu¬ 
tion progressing toward the middle 
lamella. In most of the sections ex¬ 
amined the middle lamella was appar¬ 
ently left unaffected. The entire cell 
wall was reduced to a width of 1.5 to- 
2.5 n wide as compared to 2.5 to 3.2 n 
wide in the normal wood. The walls 
show no evidence of shrinkage cracks,, 
but grooves which can be distinguished 
are apparently caused by contact with 
hyphae on their inner surfaces. A red¬ 
dish to brownish decomposition by¬ 
product is often found filling the tra¬ 
cheid and medullary ray cells. 
Following are the results of micro¬ 
chemical tests made on sections of 
infected wood of T. heterophylla and 
Abies grandis. With Millon’s reagent 
a reaction for proteins was obtained, 
in and near the zone lines and the areas 
containing these by-products. In the 
typical stage of decay such reagents 
as chloroiodide of zinc, phloroglucin and 
hydrochloric acid, potassium per¬ 
manganate, potassium dichromate, fer¬ 
ric chloride, aniline sulphate and 
paranitroaniline gave, in general, a 
reaction for the lignin compounds. 
The absence of tannin throughout the 
rotted area was also determined. In 
the bleached to white patches the 
reactions indicate that considerable of 
the cellulose compound is present. 
With tincture of alkanin slight traces 
of resin were found near the sapwood 
region. With iodine a few starch grains 
were observed in the less decomposed 
medullary rays. 
CULTURAL CHARACTERS OF DECAY 
The third step after examination for 
gross and microscopical characters of 
decay involves a cultural technique 
described in an earlier paper ( 40 ) 
Long and Harsch have shown (50) 
that cultural methods can aid in 
identifying the organism causing a 
specific decay in wood. 4 The cultural 
data on pure cultures of the fungus 
isolated from the infected wood and 
grown upon a suitable standard me¬ 
dium should include observations upon 
the source of inoculum; the macroscopic 
and microscopic characters of the 
mycelium, with emphasis upon second¬ 
ary spore formation (76 ); the size, 
color, and character of the hymenial 
layers produced in the near-typical 
and typical pilei; and conditions 
of light and temperature to which the 
cultures were exposed. To these data 
may be added proof of the important 
* An important paper by C. W. Fritz (25) has come to the writer’s attention since the preparation 
of the present papers. 
