1893.] PUBLIC DOCUMENT — Xo. 33. 213 



congenial conditions for luxuriant development. The earli- 

 est external sign of the presence of the fungus to which the 

 disease is due is commonly the appearance of dense white 

 mats of its mycelium at and near the nodes of the stem (PI. 

 I., a). Examination shows that the tissues of the stem are 

 thoroughly permeated ])y the fungus-threads, which have 

 here burst through the surface. At this stage the stem as 

 still green and plump (PI. I., a), Init as the disease pro- 

 gresses it ])egins to shrink (PI. I., b) and to turn yellow. 

 Later, its cellular tissue (parenchyma) undergoes what may 

 be termed a sort of gramtlar decay, shrivels, and finally dries 

 up, leaving hardly more than a withered mummy of the 

 original stem, consisting of the dried and yellow vascular 

 bundles and epidermis (PI. I., c). 



In the interior of diseased stems may be found thick 

 masses of white mycelium, and in the later stages there 

 appear, especially near the nodes, hard, slender black bodies, 

 sometimes of considerable size, which remain after the dis- 

 appearance of the mycelium (PI. II., fig. 1). These serve 

 as a clue to the cause of the disease when only the dried 

 skeleton of the stem remains. Sometimes similar l)lack 

 bodies are developed in the mycelial mats on the exterior of 

 the stems (PI. I., fZ), but this is not commonly the case. 

 Where it does occur, these bodies, instead of being slender 

 and spindle-shaped, are usually rounded or irregular in out- 

 line, and more or less flattened. In either form they are 

 at once recognizalile as the characteristic resting stage of 

 certain fungi, known as sclerotia, and point strongly to the 

 probability that the disease is due to one of the parasitic 

 cup-fungi (^Discomyceles) of the genus Sclerotinia . The 

 young fruits are often attacked by the fungus, becoming soft 

 and watery, and their surfaces being covered by the white 

 mycelium. The rounded and flattened sclerotia are usually 

 quite freely developed on the rotted fruits (PI. I., fi'.), 

 and are often found adherino; to their shrunken remnants. 

 Sometimes two or more sclerotia of the surface form arise 

 so close to«;ether as to become united into an irre^'ular 

 mass (fig. 2). 



These sclerotia arise from masses of fungus-threads which 



