DETAILED ACCOUNT OF SPECIFIC PLANT DISEASES 545 



producing small purple spots that are variously scattered along the 

 cane. The spots first formed rapidly increase in size, and as the 

 fungus develops the center of each becomes grayish-white in color sur- 

 rounded by a slightly raised, dark-purple border, separating the 

 healthy from the diseased tissues. The disease progresses in an up- 

 ward direction and as the advanced stage of the malady is reached, 

 the spots coalesce. The greatest injury is to the cambium, so that 

 the living tissues of the cane become sickly, the leaves do not attain 

 half their normal size, the fruit ripens prematurely, or dries up as 

 worthless. The petioles of the older leaves may be attacked and later 

 the veins of the leaves which show whitisii, blister-like spots. The 

 spots on the lamina are smaller than on the canes. 



The mycelium lives in the intercellular spaces of the host, but is 

 supplied from the neighboring host cells with nutritive materials. 

 There is at first a slight discoloration of the cell contents, the cells 

 then lose their shape and finally collapse. The conidiophores are 

 formed beneath the epidermis of the host and later appear at the 

 surface bearing the conidiospores, which are surrounded by a gelatinous 

 substance. Pruning away the diseased canes and burning them in a 

 brush heap is the most important means of controlUng the raspberry 

 anthracnose. Spraying early in the season with Bordeaux mixture 

 (4-4-50) is useful, although not an absolute preventive. 



Red Gum {Liquidamhar styraciflua, L.) 



Sap-rot {Polystictus versicolor (L.), Fr.). — Polystictus versicolor is 

 one of the most cosmopoHtan species of fungi known. It is known from 

 Europe, Africa, Australia, South America, Mexico, Japan, the West 

 Indies and throughout the United States. It grows on the sapwood 

 of every species of deciduous tree known. It is the most serious of all 

 the wood-rotting fungi, destroying probably 75 per cent, of the timber 

 used for railroad ties. A broad sheet of mycelium covers the entire 

 surface of the timber on which it grows, but it develops in the wood, 

 especially the sapwood, in which decay takes place with great rapidity.^ 

 There is a rapid solution of the various parts of the woody structure 

 for the fungus has no preference for either the lignin, or the cellulose 



1 Stevens, Neil E.: Polystictus Versicolor as a Wound Parasite of Catalpa. 

 Mycologia, vi; 263-270, Sept., 1912; see Ante p. 75. 

 35 



