i66 



CHAPTER IX 



Fig. 64 



The latest observations have been made by Stevenson in Porto Rico, 

 and he seems to consider it parasitic under certain conditions, such as 

 when the cane is weakened by drought or by excessive rainfall. He 



also observed the continual presence of the 

 fungus on the leaf sheath, and a greater 

 incidence on old cane and on young cane in 

 fields of old ratoons. 



Summing up these apparently contradic- 

 tory observations, it may be said: i. Rind 

 fungus is a condition associated with diseased, 

 dying and dead cane, characterized by the 

 appearance on the stalk of black erumpent 

 hyphae. 2. This condition may be caused [a] 

 by a single fungus, Diplodia cacaoicola, also 

 described under various other names : (b) by 

 the conjoint action of the Colletotrichum faU 

 catum and the Melanconium sacchari. In 

 this case the Colletotrichum lives in the 

 interior pith, its action being localized by the 

 protective action of the nodes to the infected 

 joint. The Melanconium fungus entering the infected joint subsequently 

 attacks the fibro vascular system, and shutting off the water supply causes 

 the rapid death of the cane. 3. The mass of evidence indicates the non- 

 parasitic nature of the Melanconium, though perhaps under certain con- 

 ditions it may become an active parasite. 4. The exact causal agent of the 

 past historic epidemics cannot now be exactly determined. 

 The technical descriptions of these fungi follow : — 



Melanconium sacchari (Massee). — Conidia produced in pycnidia formed under 

 the epidermis, unicellular, pale brown, cylindrical, straight or slightly curved. 14-15 

 X3*5-4 microns. 



Figs. 64 and 65 show a cane affected by this fungus, and the appearance 

 of the spores. 



Melanconium saccharinum (Penzig and Saccardo) .^Acervuli hypophyllous, 

 gregarious, arranged serially, oblong, i m.m. long, 0-15 m.m. wide, black, hysteroid 

 erumpent; conidia large globose-compressed, 24 microns x 14; black, smooth, borne 

 on slender filiform hyphae. 



Thyridaria tarda (Bancroft). — -Diplodia 

 cacaoicola (Henn.). — -Perithecia in a single layer 

 with seveial small ones often super-imposed, 

 immersed in a black erumpent stroma with 

 minute ostiole ; asci cylindrical-clavate with 

 eight spores, sessile, 90-100x12 microns; para- 

 physes 100—130 micron? long, abundant, filiform ; 

 ascospores monostichous, oblong, fuliginous, 

 triseptate, slightly constricted at the septa, 

 19-20 X 6-7 microns. 



Figs. 66 and 67 show, after Butler, a 

 piece of cane infected with this disease and also the Diplodia spores. 



Fig. 65 



Cytospora sacchari (Butler). — Stromatibus verruciformibus, seriatim ordinatis 

 subcutaneo-erumpentibus, pluri-locularibus, nigris, osteolo elongate, singulo, rarius 

 duobus praeditis ; sporulis minutissimis, cylindraceis curvulis, utrinque obtusis ; 

 3*5 XI' 5 niicrons ; basidiis ramosis, septatis, 12-18 microns. Hab. in culmis 

 vaginisque sacchari officinarum India. 



