164 Transactions British Mycological Society. 



Infection Experiments. 



The pathogenicity of the Rhizoctonia has been tested only 

 with material from Grevillea robusta and only with respect to 

 Coffea arahica. The work has been necessary in order to throw 

 light on a point of great practical importance to those planters 

 who have instituted Grevillea wind-breaks and shade for their 

 coffee, and it can be said that the results of the experiments 

 have supported what has been evident in the field, viz., that 

 the Rhizoctonia which has had abundant opportunity to pass 

 under natural conditions from Grevillea to Coffea arahica has 

 not yet attacked the latter host. It is necessary to distinguish 

 here between Coffea arahica, the staple crop on the majority 

 of European estates, and Coffea rohusta which is planted in 

 comparatively small, but increasing, amount, and to remember 

 that only the latter species is known to be susceptible to Rhizoc- 

 tonia root disease. 



Only healthy coffee plants in pots have been employed in 

 the experiments. The inoculum has consisted of small blocks 

 of culture medium containing active mycelium and sclerotia. 

 The fungus has been brought into contact with its intended 

 host by wrapping the inoculum around both wounded and un- 

 wounded lateral and tap-roots and also by inserting it under 

 the bark of the stem just below ground level. Sclerotia, both 

 dried and freshly taken from cultures, have been placed among 

 the roots of other plants, and pieces of Grevillea root, bark and 

 cortex containing black plates and sclerotia have been wrapped 

 around roots and also the collars of further plants. Although 

 the fungus has been allowed over eight months during which 

 to force an entrance into and obtain a footing in the tissues of 

 the experimental plants, no positive results have accrued, and 

 an examination of certain of the plants has shown their roots 

 to be unaffected by the treatment accorded them. It is to be 

 hoped that the present apparent immunity of Coffea arahica will 

 continue unabated, for, were the diseased Grevillea trees to cause 

 the death of Coffea arahica trees in contact with them, the loss 

 would be great enough to bring about a very serious state of 

 affairs on certain estates. 



The Systematic Position of the Fungus. 

 The systematic position of the fungus described in this paper 

 is somewhat doubtful. The presence of clamp-connections points 

 to its being a Basidiomycete, and the discovery of the bodies 

 presumed to be abortive basidia lends support to this view. 

 On the other hand, the absence of a fully-developed perfect 

 stage makes it impossible to refer the fungus to its correct 

 position, and the only course open in the meantime is that of 



