Florida Agricultural Experiment Station


under one tree and the infected area in the corner of this grove
adjoined a woods in which oak trees were numerous. With the
exception of one tree with a twin taproot in which one half was
dead, the main portions of the taproots on these trees were alive.
 CAUSE OF MUSHROOM ROOT ROT
 The organism causing this root rot is one of the gill fungi,
 Clitocybe tabescens (Scop.) Bres., popularly termed mushrooms
 or toadstools, which occur in clusters comprising several indi-
 viduals developed from a common base, usually at the base of
 the attacked tree (Fig. 22). This root rot closely resembles in
 many respects that caused by the well-known honey agaric or
 oak root fungus (Armillaria mellea), especially in regard to
 habit of growth, the production of rhizomorphs, appearance of
 the mushroom-like fruiting bodies, and prevalence on land where
 oak trees have occurred.
 The Clitocybe root rot fungus is propagated by means of the
 myriads of spores developed on the gills of the fruiting bodies,
 by roots of trees coming into contact with those of infected trees
 or old infected roots that may be in the soil, and by means of the
 whitish to tan-colored or brownish fungous strands or rhizo-
 morphs which are developed under certain conditions. The
 latter develop readily in artificial cultures of the fungus and fur-
 nish one of the chief means of identifying the organism before
 the mushroom-like fruiting bodies are produced. The rhizo-
 morphs are very inconspicuous and have been observed only oc-
 casionally in nature.
 Since the fungus can penetrate roots through uninjured bark
 it must be regarded as an active parasite of living trees, which is
 readily capable of spreading to adjoining trees, especially where
 closely planted. It flourishes also as a saprophyte in old stumps
 and roots of various trees, especially oaks. When the fungus
 has invaded the roots and root crown of an attacked tree suffi-
 ciently to curtail the life processes a more or less rapid decline
 of the top of the tree follows.
 The clusters of the mushroom-like fruiting bodies are pro-
 duced after the fungus has attained a certain stage of develop-
 ment, provided the moisture and temperature conditions are
 favorable. The season of their appearance in Florida is chiefly
 from October to early December. They are sufficiently dis-
tinctive so that they should not be confused with other mush-