RADIAL STPEAE (red) AM) CUNT
RESIN 'DUCTS IN WPM
August 1942
•
Tills PrID ORT IS ONE OF A SERIFS ISSUED
IC 411) THE NATION'S WAR? PROGRAM
hic. 13911
UNITED STATES DEPARTMENT OF AGRICULTURE
LLFOREST SERVICE
LFOREST PRODUCTS LABORATORY
Madison, Wisconsin
in Cooperation with the Uniirersity of Wisconsin
RADIAL STREAK (RED) .....LNIL9IANT RESIN DUCTS IV SPRUCE--
By ELOISE GERRY, Senior Microscopist
Among the less frequently encountered abnatma1ities in spruce wood
that nevertheless are of interest to inspectors of wood destined to be used
in aircraft construction are reddish radial streaks (abnormal ray tissue)
A description of these two abnormalities
and giant horizontal resin ducts
is presented here in comparison with the structure of the more normal wood.
Radial Streaks
Radir al streaks are somewhat reddish streaks, darker than the surrounding wood that, when viewed on an edge-grained face are seen to extend across
a number of annual rings. Such streaks are illustrated in A and B, figure
1. The vertical height of the streaks thus far observed is usually less
than their radial extent.
•
When the darker area, shown in figure 1, was examined under the microscope, the condition illustrated in figure 2, A and B, was found. That 18,
the wood rays in the darker area were higher vertically than normal, having
a larger number of cells one above the other. These rays are like normal
spruce rays in being only one cell wide tangentially (uniseriate rays).
The darker color of the area is due to a red gummy material in the ray cells.
In figure 2 the rays near the bottom of the specimens shown are of this
abnormal type. Here and there in addition to the uniseriate rays, fusiform
rays are found in normal spruce wood. Each contains a horizontal resin
duct, and these rays are more than one cell wide near the duct. In figure
2, A, a tangential section of spruce wood, as seen through the microscope,
is shown; at the right side an exceptionally tall fusiform ray dark with
gummy content, is present, emphasizing the abnormal condition existing
throughout the streak. Tall uniseriate, dark-colored rays are also present
above the fusiform ray as well as at the lower left side of the p)lotomiorograph, A. At the upper left corner some of the normal low uniseriate rays,
usually found in this species, may be seen.
In figure 2, B, at the bottom of the radial-section photomicrograph,
is a high ray with the characteristic dark gummy content which gives the red
1
--This mimeograph is one of a series of progress reports issued by the Forest
Products Laboratory to further the Nation's war effort. .
S
Mimeo. No. 1391
color to the streak in the wood (fig. 1, A and B). At the top of the section
in figure 2, B, the colorless appearance of the ray cells, as ordinarily
found, is shown.
No evidence has been obtained to indicate that these darker streaks,
as illustrated, are in themselves a source of weakness in the wood. No
indication of the presence of fungus was found.
To date no material showing the cause or beginning of one of these
areas has been available for examination.
Giant Resin Ducts
Resin passages or ducts with their length radial and diameter up to
about 1/e8 inch, so large that they are easily seen by the naked eye, and
consequently have sometimes been mistaken for wormholes, may occur in spruce
wood. These are shown in figure 1, C and D; as seen on a tangential (flatgrained) surface, they appear as approximately round spots or openings.
Their appearance as seen through the microscope is shown in figure 3, A, B,
and C, and 4, A and B. In the photomicrographs the giant horizontal resin
passages may be compared with the normal vertical resin ducts. In figure
4, A and B the varying sizes of horizontal resin ducts ranging from normal
size NRD, figure 4, A, to giant size are shown. At the left in figure 4, A,
a rather large vertical resin passage is shown. From both A and B it is
evident that resin ducts may be found with an open passage at the center or
this may be closed to varying degrees by the parenchymatous tissue characteristic of resiniferous growths in spruce.
In determining when wood with giant resin ducts should be rejected,
the strength requirements of the part and the number of ducts present per
unit area should be considered. Since the resin ducts do not produce
serious distortion of the grain, their presence in low – stressed parts is,
unless in obviously large numbers, not objectionable, and, even in highlystressed parts, the presence of occasional large ducts should not be cause
for rejection.
No. 1391
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Figure 3.--Giant ray resin ducts. A and B show transverse sections with abnormally
large horizontal resin ducts. These contrast markedly with the small
normal vertical resin ducts which are usually larger in diameter than
the horizontal ducts.
0, Radial section showing a giant horizontal resin duct crossing several
Z M 42741 F
annual rings; it also crosses an ordinary vertical duct in the ring
at the extreme right.
Figure 4.--Giant ray resin ducts. A and B show tangential sections containing giant
ray resin ducts and other horizontal resin ducts of varying sizes. At
NRD is shown a normal horizontal resin duct in a fusiform ray. A giant
Z M 4 2742 F
resin duct with open passage is shown at G.