Brown rots have a shrunken cubical appearance. Brown rots occurs mostly in gymnosperms and in wood products. Lentinus lepideus, and Polyporus betulinus. Polyporus sulphureus and Fomes pinicola are examples of fungi that cause the less common brown rot in angiosperms. The S 2 layer of the middle cell wall is digested by some microorganisms.
Many variations occur.
The causal fungi are usually nonhymenomycetes- Phialophora, Penicillium, Chaetomium , etc. Soft rots occur mostly in moisture-saturated angiosperm wood products. Little is known about soft rots in living trees. Little is known yet about the effects of bacteria alone on wood. In ponded logs, bacteria do invade pits-mostly the microfibrils of the pit margos.