TAUBENHAUS: SILVER SCURF OF THE WHITE POTATO 557 



zones (figs. 9 and 10). The organism too, is a vigorous grower, 

 compared to Spondylocladium atrovirens, the latter of which forms 

 small colonies which are seldom larger then one third of an inch 

 in diameter (fig. 6). Colletotrichum atramentarium will grow 

 and increase in zonation as far as space permits in the petri dish 

 (figs. 9 and 10). 



How SILVER SCURF IS CARRIED OVER. — Silver scurf is carried 

 with the seed and with the soil. To prove this, a number of 

 tubers which were infected with silver scurf were planted in a clean 

 soil in the greenhouse. In another lot, a pure culture of the 

 fungus Spo7idylocladium atrovirens Harz was mixed with clean 

 soil, and healthy disinfected tubers planted therein. Healthy and 

 disinfected tubers were also planted in clean soil to serve as 

 checks. The plants in all the lots grew well, and in four months 

 mature hills of potatoes were formed in each lot. The results 

 showed that the lot infected with a pure culture of S. atrovirens 

 produced 100 per cent diseased tubers. Where infected seeds 

 were used, the new tubers showed 60 per cent infection. All 

 the checks were free from the disease. A second crop of potatoes 

 was grown on the same plots. In this case, however, only 

 healthy disinfected seeds were planted. At the end of the experi- 

 ment, the tubers in the check plot were all healthy, while those in 

 the other two plots were infected with silver scurf. This clearly 

 shows that the seed as well as the soil, is a carrier of the disease. 

 There is no doubt but that the fungus Colletotrichum atramen- 

 tarium, like Spondylocladium atrovirens, is also carried by the above 

 two agencies. In the plot where only infected tubers were planted, 

 Colletotrichum atramentarium was also present on the spots of the 

 new crop as well as on the dying vines. 



Pathological morphology. — Silver scurf is only an epidermis 

 disease (fig. ii). At no time has the writer been able to find 

 evidence that the fungus Spondylocladium atrovirens Harz is 

 capable of producing a scab, or a dry rot. Wherever such cases 

 came to our attention, the material was immediately cultured, 

 and the resultant flora was rich in Actinomyces, Fusaria, and other 

 Hyphomycetes, but not with Spondylocladium atrovirens. The 

 same is also true for Colletotrichum atramentarium (figs. 12, 19, 

 20, and 21), with the exception however, that the latter is capable 

 of entering deep into tubers which have previously rotted by other 

 organisms, such as Fusaria. 



