A Rhizoctonia causing root disease in Uganda. W. Small. 153 



occurrences of the Rhizoctonia on tea and amatto [Bixa Orellana 

 L.) are discussed later. The fungus has also attacked Casuarina 

 equisetifolia and Coffea robusta ; which latter is grown on certain 

 estates in addition to C. arabica. Attention may be drawn to 

 the fact that the Rhizoctonia has occurred only on introduced 

 Coffea robusta (originally from Java), and that none of its five 

 hosts is indigenous to Uganda. It may be mentioned that this 

 is the first record of a species of Rhizoctonia in this part of 

 Africa. The present species is e\idently widespread in Uganda, 

 for cases of its parasitism have been noted in districts far- 

 removed from each other. 



Symptoms of the Root Disease of Grevillea Robusta. 

 The browTiing and wilting of part of the foUage of a tree is 

 the first s\"mptom of attack and consequent disease, but it 

 frequently happens that blackening of areas of the trunk 

 followed by exudations of a resinous or gimim\^ substance from 

 the trunk and larger branches, if the tree is an older one, is 

 the first cause of attention being drawn to its abnormal con- 

 dition. Subsequently, certain upper branches or shoots may 

 become leafless, and a "stag-horn" condition may be apparent. 

 It has been customary to refer to this effect of the root disease 

 as "die-back." Xectria floccidenta v. Hoehn. and a species of 

 Phoma may be found on the dead and d\ing twigs, but these 

 fungi have been shown to be merely saprophvtic. In addition 

 to the cracks in the trunk, others appear at the collar of the 

 tree, which also may give rise to streams of gum, and lead 

 eventually to the scaling of the bark. At this time, a cut into 

 the bark and cortical tissues discloses a certain amount of dis- 

 coloration which microscopic examination shows to be accom- 

 panied by internal accumulations of gum, and an examination 

 of the cambial tissues shows that they have entirely broken 

 down. No h\-phae have been found in association with the gum 

 in the stem more than a few inches above the coUar, but 

 mmierous and characteristic oil-globules exude from sections of 

 all the degenerating tissues. In young diseased trees, suckers 

 often sprout from the base of the trunk, and cases are known 

 in which a sucker has grown to be as large as the original stem 

 of the tree before death ensued. It is likely, therefore, that the 

 progress of the disease is slow, but there is, unfortunately, no 

 doubt about its eventual result. 



\Mien the underground parts of a diseased tree are exposed 

 by excavation, s\Tnptoms of the root-disease may not obtrude 

 themselves at once on the investigator. In fact," if the case of 

 disease is of short standing, the roots of the tree, except for a 

 sHght, superficial blackening of the smaller ones, may appear 



