Page:Popular Science Monthly Volume 29.djvu/628

 The affected wood looks dark and moldy, and, upon close examination, the little beaks, about one eighth of an inch long, can be seen projecting from the wood, and, when it is dressed, will show discoloration; if dried, the further growth of the fungus is arrested, but will be resumed if the wood becomes damp. On examination with the microscope, the resin-ducts of the medullary rays (see Fig. 11) will be found filled with the dark-colored threads, spreading to the upright ducts and the wood-cells. Although the dark threads are abundant, discoloring the wood, they alone do not destroy the canals, but are aided by fermentations.

Fig. 18 shows some of the cultivated ferments I obtained from splitting open a block and touching a sterilized needle to a resin-duct destroyed by Sphæria pilifera (Fr.), and then inoculating a culture-tube of prepared gelatine. It will be recognized as a species of Saccharomycetes, but with more elliptical cells than Saccharomycetes cervisiæ, the yeast-plant. In wood further advanced in decay than the destruction of its resin-ducts, rounder cells have been frequently obtained by direct observation with the microscope.

Some species of the Sphæria played important parts, infinitesimal though they were, in inducing the fermentations which helped decay the Nicholson pavement; for in the partially decomposed white-pine blocks I find generally an abundance of the dark hypha, and, in some, the fragments of perithecia, showing it was a Sphæria that produced the dark filaments, and not a modification of the white mycelia of some of the higher fungi which are often found associated with it, or in other portions of the block. The decayed spots in the white cedar before described are more or less filled with the dark-colored hypha of some species of Sphæria.



Fig. 19, magnified ten diameters, represents Sphæria aqitila (Fr.), "Brown nestling Sphæria," very common on limbs on the ground—the mycelium pierces and discolors the wood-cells. An asci containing the ascospores, magnified fifty diameters, is shown in the left side of the figure.

Sphæria morbosa causes the black knot in plum and cherry trees.

In Fig. 20 are represented a few of the filaments and the dark