DISEASES AND ENEMIES 243 



The " white-root fungus " (probably Fomes semi- 

 tostus) is more harmful to the Para rubber tree (Hevea 

 brasiliensis), to tea, to cinchona, and other plants in 

 Java, Sumatra, the Straits, and Ceylon. Now and 

 then it does some harm to the cocoa trees, but almost 

 always only in fields recently established on virgin 

 land. 



The fungus appears as a white felt-like cover on the 

 roots ; it seems to dislike the deeper layers of the soil, 

 and appears principally on the main root, not far from 

 the surface of the soil, and on the larger side roots near 

 the junction with the main root. Along these parts 

 it creeps with its mycelium in the form of irregular 

 threads and patches, extending not only over the roots 

 and sometimes the basal part of the stem, but also 

 through the surrounding soil, binding together the 

 particles of earth so that they remain adhering to the 

 roots when the tree is dug out. The fungus simply 

 kills the trees without causing characteristic symptoms. 



A similar root disease has been found in Samoa, 1 

 New Guinea, Ceylon, and West Africa ; the fungus 

 resembles the one just mentioned, but the mycelium 

 is more or less yellowish or even brownish, and belongs 

 to another species (Hymenochaete noxia). It has caused 

 much damage in Samoa. 



On the Antilles different root diseases have been 

 observed. A "white-root disease" and a " black-root 

 disease" have been described by South (West Indian 

 Bulletin, vol. xii. 1912, p. 479). The fungi which cause 

 these diseases have, however, not yet been identified. 

 A "Thyridaria root rot" has also been described : it has 

 been attributed to Diplodia cacaoicola ( = Thyridaria 

 tar da], but this still requires confirmation. 



The root fungus of Kamerun has been described 

 by von Faber. 2 The symptoms of the disease are 

 the same as those of the "white-root fungus" of Java, 



1 Preuss, Beihefte zum Tropcnpflanzer, vii. (1907), p. 71. 



2 Von Faber, "Die Krankheiten und Parasiten des Kakaobaumes " (Arb. 

 Kate. Biol. Anstalt, 1909, p. 223). 



