538 
Yol. XXIX, No. 11 
Journal o f Agricultural Research 
stroyer. So-called medallion hyphae 
are common to Lenzites spp. {22). 
Granular deposits on the outer walls 
of the hyphae are characteristic of 
certain species of Peniophora or Conio- 
phora and sometimes of Lentinus 
lepideus {11 , 22). 
The order of dissolution of the cell 
wall may often suggest the type of 
decay. If the primary wall is resistant 
the bore holes may be constricted (19 
in fig. 6). Spiral cracks in primary and 
secondary walls and bore holes or cell- 
wall punctures are often reliable 
characters; also spiral shrinkage^ cracks 
extending from pit openings or bore 
holes (fig. 5, E, F). The latter have also 
been found in wood in which hyphae 
were absent. If it is proved that these 
cracks are due to fungous action, their 
presence in tissues lacking hyphae of 
any kind may point to enzymic action 
some distance removed from the 
secreting hyphae. Corrosion marks, 
grooves, uneven surfaces, and uneven 
thicknesses of cell walls, splitting of 
middle lamella, and dissolution of ter¬ 
tiary layer are all good' indications of 
decay. White {89) considers over¬ 
abundant formation of tyloses in the 
region of incipient decay, and none in 
the sound region beyond, a safe cri¬ 
terion of the presence of a parasitic 
wood-rot fungus. Wound gum depos¬ 
its in the region ahead of hyphae are 
often characteristic signs. Calcium 
oxalate crystals deposited on the cell 
walls and in form resembling hyphae 
may indicate {Lentinus lepideus) hyphae 
which have been decomposed {11). 
Other reliable signs of decay are the 
enlargement of pit openings, corrosion 
and cracking of bordered pits, and 
presence of granular deposits or corro¬ 
sion marks on the scalariform bars at 
ends of vessels. The accumulation in 
the bordered pits of by-products and 
resins in certain woods should not be 
confused with corrosion marks often 
seen on the embossed portion of these 
pits. 
Corrosion, thinning, and entire de¬ 
composition of the cross walls are 
prominent decay characters in the 
medullary rays. Whether pit openings 
or bore holes are used as channels for 
hyphae may aid in distinguishing wood 
destroyers from staining or molding 
fungi. In the ray cells, decomposition 
products, wound gum, granular depos¬ 
its, and tannin are often of diagnostic 
significance. Where the enzyme amy¬ 
lase is produced the starch grains are 
corroded or are partly or completely 
dissolved. The effect upon the wood- 
fiber cell walls of a decay-producing 
fungus is well illustrated in Plate 6. 
A tranverse section of the wood of 
Ulmus americana infected with a white 
rot fungus in which the fiber walls are 
remarkably reduced is shown at A, 
while B shows a transverse section of 
the normal uninfected wood of Ulmus 
americana with thick fiber walls. 
Color reactions produced in micro¬ 
scopical sections by different chemicals 
as indicators of the presence or absence 
of lignin or cellulose compounds in the 
infected tissues are useful in decay 
diagnosis and in a study of the micro¬ 
scopical characters of particular wood 
rots. Many such chemicals are given 
by Crocker {18). The writer has 
found the following of value also: 
Para-nitroaniline and hydrochloric acid, 
producing a bright orange yellow; 
pyrrole, producing a deep red; diphe- 
nylamine, producing an orange yel¬ 
low; and both metol and hydro- 
quinone, giving a light yellow color 
reaction. 
For testing the presence of cellulose 
the iodine compounds giving violet to 
blue reactions are often helpful, also 
sulphuric acid and cuprammonia. A 
test for tannin is sometimes of value, 
as tannin is often found in decayed 
wood and absent in sound wood of the 
same species. Tubeuf {79, p. 40 ), using 
the ferric chloride test, found no reac¬ 
tion in sound spruce wood but secured 
a reaction for tannin in the same wood 
infected with dry rot produced by 
Merulius lachrymans. The standard 
stains used in microscopical technique 
serve to determine the constituents or 
the layers of the cell wall first attacked 
and whether dissolution is from within 
the cell outward or the reverse. The 
action of the fungus on the middle 
lamella as determined by staining is of 
particular value, as shown by the work 
of Spaulding (77). 
It has been extremely difficult in the 
microscopical examination to demon¬ 
strate the presence of fungous hypae in 
the wood tissues. They are very small 
and quite transparent in the incipient 
stages of many rots, and are easily con¬ 
fused with hyaline fragments of the 
wood cells. The methyl violet Bis¬ 
marck brown method for staining 
EXPLANATORY LEGEND FOR PLATE 6 
A.—Photomicrograph showing transverse section of Ulmus americana infected with a wood-destroying 
fungus. Note the thinness of the wood fiber cell walls. X50. B.—Photomicrograph showing transverse 
section of sound Ulmus americana. The thickness of the normal wood fiber cell walls are very pronounced. 
X50. (Courtesy of Mr. Koehler.) 
