68 



FUNGOID DISEASES 



crops than is generally imagined, for only when it 

 breaks out as an epidemic is any notice taken of it. 

 Symptoms . — The attacked plants turn yellowish 

 without any visible sign of the cause, and gradually 

 die off. On examination of the dead parts, especi- 

 ally the root and part of the stem at, or near, the 

 ground surface, the sclerotia may be seen as small 

 black button-like growths (Fig. 19, A, sc). 



Fig. ig. — Sclerotium disease of clover: (A) portion of clover root with 

 sclerotia {sc) attached ; (B) a sclerotium germinating ; {t) the 

 trumpet-shaped stroma containing the spores ; (s) the soil level. 

 (After Frank.) 



Cause.— ^\\^ cause of the plants dying is the 

 presence in their tissues of the fungus Sclerotinia 

 Trifoliorum. This mycelium absorbs its food 

 supply from the clover plant, thereby causing 

 gradual starvation. The plant ultimately dies and 

 shrivels up, and the fungus, in order to prepare for 

 emergencies, forms sclerotia. These sclerotia can 

 rest over winter, in fact are capable of growth after 

 being kept dry for two or three years. Under 



