A cut in a growing tree will be healed over in a few years, and in many woods, after twenty-five to thirty years, the scar can hardly be found. This fact will be recognized by those who have traced former land-surveys through the forests; upon rerunning the line, chopping into a supposed line-tree is often required to determine the question, the former wound having healed so perfectly as not to leave a scar.
Fig. 16, one fourth size, represents Polyporus pinicola (Fr.), partly in section to show the pores, also the apparent economy in the use of material in providing a surface for the growth of the spores, a succeeding forming over a preceding growth; on the upper portion the spore-bearing surface was renewed three times, and then new tissue pushed out underneath, and one set of pores formed before it was gathered. This fungus is found upon the firs and spruces, and is very destructive to planks of the latter, destroying those of two inches in thickness, in walks in from two to four years, while in station-platforms close to the ground, they do not last that length of time. One interesting feature in regard to this fungus is the quantity of phosphoric acid which was obtained from it by treating with necessary reagents. Potash and lime were also abundant. The watery extract from this fungus nearly resembles in composition the artificial preparations used for the cultivation of molds, and it undergoes fermentation in a few hours in the laboratory, cells of some of the species of Saccharomycetes growing in great abundance. In wood in process of destruction by this fungus, similar cells have been found.
The fungi so far illustrated are but a few of the species of the highest types which produce the so-called "dry rot" in timber, and the list could be extended, though the final results of all are practically similar, all requiring about the same general conditions for growth in order to destroy the timber. Besides those of the highest type, there are many other fungi, which are very destructive. The lower order of Sphæriacei contains some genera which are parasitic upon the trees, especially the Sphæria; others of its species thrive upon decorticated trees and unseasoned sawed timber, and many are associated with the decay of timber that writers have called "wet rot." The distinction from the improperly called "dry rot" is not clear, as in either kind the presence of moisture, air, and warmth combined is essential.
The mycelia of the Sphæria are not so abundant as those of the higher types, but the filaments are larger, stronger, and able to pierce the medullary cells of the sap-wood, destroying them and making a free entrance for air and moisture. Fig. 17 represents Sphæria pilifera (Fr.), as identified by Professor Charles H. Peck, and is drawn from specimens I have found abundant upon the sap-wood of the yellow pine from the South, as stated in the former paper; another form of it is sometimes found from the same locality, having smooth perithecia; this latter form is common in the white pine in Massachusetts.
