SILVER SCURF, A DISEASE OF THE POTATO. 



17 



faces of ]-)Otatoes. As the fungus spreads in the tissues it loosens the 

 surface lavers, causino; the wliite silvery color. Later the surface lay 

 ers slouo-h off, carrying with, them numerous sclerotia that infect the 

 soil. In moist conditions the fungus fruits in from four to five days 

 after the spores have germinated. The conidiophores may spring 

 either from the mycelium in the tissues or from a sclerotium, in the 

 manner shown in figure 1, a. The conidiophores are dark brown, 





i'f 



Fig. 2.— Potatoes (Irish Cobbler variety) infected with Spondylocladium atrovirens. The lower right-hand 

 tuber is irse from infection, while the other two show successive stages of infection. The diseased areas 

 in this stage of development have not become shrunk and shriveled. 



rather tall, being about 120 microns long and 4 microns in diameter. 

 (See fig. 1.) The spores are Dorne in rather irregular whorls on the 

 upper portion of the conidiophore. The spores are dark browm, obo- 

 vate, 5 to 7 celled, and about 40 microns in length by 8 in diameter. 

 Nothing is knowai as to the longevity of the spores or the sclerotia. 

 It is very probable that both are f|uite resistant and may therefore 

 be important factors in facilitating the spread and continuance of 

 the disease. It has been shown by Eichinger that the germ tubes 

 and mycelium grow from the light, showing a negatively heliotropic 



reaction. 



91517°— Cir. 127—13 3 



