3o8 DISEASES OF CROP-PLANTS 



each cutting gets its share of the precipitate, (3) the drying of 

 the cuttings to allow the film to set, and (4) careful subsequent 

 handling so that the film is preserved. 



DiPLODiA Rot. 



The fungus Diplodia Theobromce (Pat.), common throughout 

 the tropics as a weak parasite and as a saprophyte on the branches 

 of various trees, occurs also on sugar-cane. A. Howard described 

 it on this host in Barbados and British Guiana, and E. J. Butler 

 has found it to be not uncommon in India. Although Howard suc- 

 ceeded in infecting healthy canes with the fungus it appears from 

 general experience to resemble Melanconimn Sacchari rather than 

 the active parasites in the nature of its occurrence. It bears 

 a close resemblance to Melanconium in general appearance also, 

 and it is not always easy in the field to discriminate between 

 them. Under the microscope the spores of Diplodia are at once 

 distinguishable if mature by their two-celled condition. The 

 small and crowded pycnidia occur just under the rind, mostly 

 about the nodes. The little swellings which mark their position 

 open with a tiny longitudinal slit, from which the spores are 

 extruded. The interior of the affected cane takes on a general 

 red discoloration, and later becomes darkened by the presence 

 of the mature mycelium. 



The fungus is mostly found on over-ripe canes or such as have 

 been seriously damaged or killed by borer or other means. 



Wilt Disease. 



This disease was first described by E. J. Butler in 1913 from 

 India, where it was discovered during the investigation of red-rot. 

 It is found to occur over a large part of India, generally mixed 

 with red-rot, but sometimes doing considerable damage where the 

 latter is not present. As a rule the disease has not proved 

 serious in its effects. 



An affection having characters which so far as they can be 

 judged by figures and descriptions are identical with those of the 

 Indian disease has been detected in Barbados and in Nevis. 

 Over a fairly wide area in Barbados in 1915 it occurred in con- 

 siderable quantity in some fields. Very little further spread 

 was noticed and the final result on the crop was not important. 

 The most probable explanation of its occurrence to this marked 

 extent was that the canes attacked had been somewhat damaged 

 by the wrenching action of high winds experienced some time 

 before. Infestation of the stools with Marasmius also seemed 

 to function as a predisposing cause. The circumstances under 

 which the fungus is occasionally found suggest that normally 

 it is present in scattered infections of borer holes. 



