14 BULLETIN 1380, U. S. DEPARTMENT OF AGRICULTURE 
tions appear on the bark as small protuberances, which are white 
when in a growing condition. These projections begin to expand at 
the margin, and eventually broad flat plates some 4 or 5 centimeters 
in diameter and about 2 millimeters thick are developed and are 
attached only at the point of origin. Most of the black incrusting 
fungi of this group are attached to the substratum over their entire 
lower surface and are consequently more firmly fixed. When several 
plates develop in close juxtaposition their margins fuse and a crust 
may be formed over a considerable area. Each individual plate is 
usually concentrically zoned, so that the compound plate appears to 
be made up of a series of circular disks. With age these plates may 
become undulated or corrugated as growth ceases. The edges may 
remain very thin. At first white or gray, the plates on weathering 
or when old become black. When fully mature the plates are white 
internally and usually show a' single layer of elongated or oval 
cavities (perithecia) (PL V11T. A) filled with a plastic content. 
When old the cavities become empty and the tissues turn black and 
are very brittle. 
The fiat plate with concentric zones is not always a constant char- 
acter of the fungous fruits on uneven surfaces. The fructifications 
may be wry irregular, without' zonations, and may resemble other 
species of the group. UstvZina vulgaris (PL VIII, C) of the Tem- 
perate Zone is said to be identical with U. sonata. 
The upper surface of the crust is dotted with numerous small 
black points (ostiola). Each of these corresponds to a cavity below 
and is the opening through which the spores are expelled. In the 
early stages of development, before the cavities are formed, the sur- 
face is covered with numerous conidial spores borne on short erect 
stalks. These spores are the first to be developed and, since they 
may be carried about by the wind, serve as a ready means of dis- 
tributing the fungus. The production of conidia soon ceases, and 
the surface becomes hard and smooth with the exception of the small 
punctations which open into the cavities. The second spore formed 
is produced in asci lining the walls of these cavities. These spores 
are dark colored and spindle shaped, and they are expelled through 
the ostiola. During damp weather they may collect in the form of 
a black deposit on the surface of the crust. 
The progress of the disease appeared to have been very slow. 
At the time of study the edges of the canker were beginning to 
put out healing tissue. The internal activity of the fungus ap- 
peared to be somewhat diminished, in that the line of demarcation 
between the infected and the sound wood was sharply defined. The 
cortex of the infected roots for several inches below the canker 
was of a bluish black color. Mycelial fans bounded by black lines 
were present on the under surface of the bark or on the wood of 
the root. The latter condition appears to be more or less char- 
acteristic for the disease, not having been noted in other fungi 
of this group on Hevea. The presence of black lines in the wood, 
however, is misleading. These lines are common to a large number 
of Pyrenomycetes. 
It is unlikely that the fungus can enter the tree without the 
intervention of wounds. These are more likely to be at the base 
of the tree. Although one case was noted where tapping wounds 
