FENCE POST-ROT 
One of the items of expense on the farm is the building and keeping up 
of fences. The life of the posts is considerably shortened by various 
saprophytic fungi which often attack and quickly rot them. A knowledge 
of the character of these rots and of the conditions favorable to them 
is of service in devising means of treatment which greatly lengthen the life 
of the timber. 
SYMPTOMS 
Sections of affected timber are provided. OBSERVE:— 
1. The light-colored region about the margin, inside of the bark, 
—the affected wood. Compare the hardness of this with that of healthy 
wood. Is the bark similarly affected? 
2. That the affected wood in the early stages includes only 
the outer three or four annual rings, but that ultimately the penetration 
is deeper, showing that although the sap-wood is first invaded the heart- 
wood will finally also be destroyed. Compare with the blocks that have 
been affected longest. 
Make prawincs of the transverse and longitudinal aspects. 
3. On the larger blocks, the shelving or resupinate sporophores 
of the fungus causing this decay. Why are some shelving and some 
resupinate? Make an outline DRAWING showing these sporophores 
attached to the post. 
ETIOLOGY 
The cause of this rot is a very common polyporaceous fungus, Polysttc- 
tus versicolor (Linneus) Fries. The fungus is ordinarily a saprogene 
but is known to cause destructive heart-rot of catalpa. It attacks a great 
variety of timbers of broad-leaved trees but never affects coniferous wood. 
Life-history. There are apparently no secondary cycles, the infection 
occuring in the earlier part of the season with usually no production of 
aaa until the end of the season. There is of course no pathogenic 
phase. 
The Life Cycles are initiated by basidiospores from the fruit-bodies 
during the wet weather of spring and early summer, and possibly also to 
some extent from early-matured sporophores in the autumn. 
Saprogenesis. Examine the black paper under the sporophores 
which have been in a moist-chamber for several hours. OBSERVE:— 
4. The tiny piles of white spores, each representing the spores 
discharged from a single pore. 
Mount some of these spores in water and examine under high-power. 
OBSERVE :— 
5. Their form, size, color and contents. pRaw. Study and 
DRAW to show spore-germination as seen in slides provided. 
The germtube penetrates to the dead sap-wood, where it develops 
a vigorous mycelium. This mycelium spreads through the wood, dis- 
integrates it by means of enzymes and feeds upon the products of this 
disintegration. 
Study a thin longisection of the diseased wood and OBSERVE :— 
6. The mycelial threads, especially abundant in the pitted vessels 
and medullary rays. 
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