300 



the inost part confined to the skin, and though the flesh of the 

 tuber is penetrated to a slight extent by the fungus, it entails no 

 appreciable waste in peeling. Beyond, therefore, rendering the 

 tubers unsightly, and thus somewhat reducing their market value, 

 this form of injury is not great. 



In the case of seed potatoes, however, Skin Spot is of con- 

 siderably more importance. When a crop in spring shows much 

 infection, or the spots on the tubers are closely crowded together, 



there is a great danger of the eyes being injured. If the eyes are 

 unaffected the shoots will grow and the plants will yield a normal 

 healthy crop. This has been proved during two consecutive seasons 

 at Kew. It should be remembered, however, that if the soil be 

 suitable for the fungus it may become infected and future potato 

 crops will be liable to suffer. On the other hand, where infection 

 has taken place in the neighbourhood of the eyes, the eyes are 

 definitely injured and even killed. This form of injury was 

 stated to take place by Milburn, though no details as to the nature 



of the injury are given. It was also noted by Mr. F. T. Brooks 



and Miss A. D. Mackenzie, and also by Miss K. Sampson. Ex- 

 amination of tubers affected at the eyes shows that the fungus 

 appears to penetrate, particularly deeply, the tissues around the 

 eyes, and that in many cases relatively large areas of tissue may 

 be killed. It has been observed by means of sections that the 

 fungus at times not only kills the tissue around the eye, but also 

 that immediately below it, Oospora pastulans has been isolated 

 from a number of eyes killed in this way. As will be obvious 

 from the earlier part of this paper, the details of infection were 

 not ascertained, but there is no evidence at present that infection 

 takes place more readily at the eyes than elsewhere. From these 

 observations it would appear that Milburn 5 s conclusion (p. 91, 

 footnote) that it was the Skin Spot fungus which killed the eyes 

 of several tons of " Evergood " was quite likely to be correct. 



Although the primary eyes may be killed, it sometimes happens 

 that secondary eyes may develop. Tubers of "King Edward,' 7 

 most of the eyes of which had been killed by Oospora, were placed 

 in boxes to sprout in the usual way, and it was found that of the 

 injured and killed eyes about 45 per cent, developed secondary 

 eyes. Sections through some of these showed that the new buds 

 had pushed their way through the dead tissue. This method of 

 development has been described bv Goebel (Einleitung in die 

 Experimentelle Morphologie der Pflanzen. 1908. pp. 221-222). 

 These new buds appeared to be f airlv strong and their production 

 affords an explanation of a phenomenon noted when badly spotted 

 tubers were planted at Kew, namely, that all the tubers developed 

 strong plants. On account of the check at the start, however, the 

 plants would be later, and the yield perhaps somewhat less. 

 Though these secondary eyes are undoubtedly developed fairly 

 frequently, many eyes are killed outrigjit, and if it can be avoided 

 it is highly undesirable to plant badlv spotted tubers. From the 

 remarks made by Giissow (see p. 492), it is possible that the 

 development of Skin Spot is favoured by bad ventilation during 

 storage, but from observations made in England last year it is 

 clear that Skin Spot is often entirely absent in very badly venti- 







