CHAPTER III 



OMPHALIA FLAVIDA, A GEMMIFEROUS AND LUMINOUS 



LEAF-SPOT FUNGUS 



Introduction — OmpJialia flavida and the American Coffee-leaf Disease — Stilhum 

 flavidum as a Stage in the Life-history of Omphalia flavida — The Structure 

 of the so-called Stilbum-hody — The Omphalia flavida Sporophore — The Origin 

 of the Stilbum-hodies — The Stilbum-hody as a Gemmifer — The Basal Curvature 

 of the Pedicel and its Significance — The Sigmoid Curvature of the Pedicel and 

 the Abscission of the Gemma — The Detachment of a Gemma from its Pedicel 

 — The Attachment of a Gemma to a Leaf — Mode of Germination of a Gemma 

 — The Effect of Desiccation on the Vitality of a Gemma — Inoculation Experi- 

 ments with Living Leaves — Omphalia flavida as a Non-specialised Parasite — 

 Sterility of the Mycelium Induced by Prolonged Cultivation on Artificial Media 

 — The Effect of Light on the Formation of Gemmifers — Luminescence of the 

 Mycelium and its Value as a Diagnostic Character of the Coffee-leaf Disease — 

 The Gemmifers of Sderotium coffeicola. 



Introduction. — Oniphalia flavida is a Hymenomycete of peculiar 

 interest in that : ( 1) it is a parasite which is able to attack the leaves 

 of a great variety of plants ; (2) it reproduces itself not only by 

 means of basidiospores but also by means of gemmae of unique 

 structure (the so-called stilbum-hesids) ; and (3) its mycelium is 

 luminous. 



Omphalia flavida and the American Coflfee-leaf Disease. — 

 Omphalia flavida first attracted attention owing to the fact that, 

 under very moist climatic conditions, it causes a serious leaf-spot 

 disease of the Coffee tree (Figs. 198, 199, and 200). The disease 

 has been reported from Mexico, Central America, the Antilles, 

 Trinidad, Venezuela, Brazil, and generally throughout the coffee- 

 growing region of America, ^ and it has therefore been called the 

 American Coffee-leaf disease.^ 



^ G. L. Fawcett, " Fungus Diseases of Coffee in Porto Rico," Porto Rico Agri. 

 Exp. Station, Bull. No. 17, 1915, p. 11. 



2 S. F. Ashby, " The Perfect Form of Stilbum flavidum Cke. in Pure Culture," 

 Bulletin of Miscellaneous Information, Royal Botanic Gardens, Kew, 1925, p. 325. 



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