Page:Popular Science Monthly Volume 29.djvu/457

Rh moisture accumulated where it rested on the joists, the mycelia working upward and each way, usually leaving a thin portion of one eighth to one fourth of an inch in thickness, on the under side of the plank, where exposed to the air, giving the appearance that it was all sound. The abundant fructification during a brief warm rain in September, 1883, was the first indication of the destruction which had taken place.

The upright cells or tracheids composing the annular ring of the Pinus palistris (Mill) are of two kinds—one of thin and the other of thick walls; the former fill the inner part of the ring, the latter the outer portion, giving the great strength and hardness characteristic of this wood; interspersed through the ring are a few resin-ducts. In decay induced by its special fungus, the mycelium often separates some of the annual layers, and in most cases the thin-walled cells are first softened. Driving spikes into railroad-ties of this wood breaks and loosens the layers, and facilitates the entrance of the mycelium, and then larvae, from one sixteenth to one eighth of an inch in length, eat and bore in the large softened tracheids, leaving the harder ones, so that in ties of four to seven years' service we often find little more than a series of nearly separated shells. The mycelium of this fungus once in a road-bed lives for some time, and in summer is ready to attack new ties of this timber as soon as put in the ground. I have noticed ties taken up, after a short service of six to eight months, which were covered on the bottom by the branching mycelium, and after drying one eighth to one fourth of an inch in depth would crumble to dust. It takes much longer for the mycelium to destroy the heart-wood of the yellow-pine sleepers from the bottom and sides than when it has access to the ends. In the first case it must nearly destroy the small medullary cells to reach the various rings, while from the end it has a larger area of the rings, which it readily follows. Painting the ends of this timber offers but little protection if the slightest opening occurs, as a spore can enter, grow, and carry on its destruction for a long time before it shows exterior decay.

The mycelium of Lentinus lepideus (Fr.) is composed of small branching filaments, only measuring 0·0004 of an inch to 0·0008 of an inch in diameter. With it I generally find an abundance of crystals of one form of oxalate of lime, and many cells of other fungi in adherent masses. The destructive power of this fungus is very great, and is causing enormous losses to consumers of the yellow pine, which are not realized or even suspected. In the sap-wood of this timber the fungus Sphæria pilifera (Fr.) readily grows, piercing the resin ducts in the medullary rays, its hyphæ spreading to the upright resin canals, and, from its abundance and dark color, discolors this portion of the wood; which, if it remains damp and warm, the fermentation set up soon destroys the sap-wood. This fungus grows at a very low temperature, and is very destructive.

In new railroad-ties of yellow pine, which came from Georgia