42 



JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 



EXPEEIMENT I. 



Seed potatos of the varieties ' Up-to-Date ' and ' Northern Star,' 

 raised in Scotland, and of the varieties * Northern Star ' and * British 

 Queen,' raised in Cambridgeshire in 1907, were planted in the garden 

 of Armstrong College, Newcastle-upon-Tyne, on May 4, 1908. The 

 soil was comparatively poor, dark garden soil, and was not heavily 

 manured. The crop was lifted in September, but when examined was 

 found entirely free from any disease. 



Experiment IL 



Potatos of the variety * British Queen ' obtained from the county 

 of Durham, badly affected with a black discoloration of the flesh, 

 as show^n in the illustrations (fig. 21), were planted some in Devon- 

 shire and some in the garden of Armstrong College. The con- 

 ditions in the latter locality were similar to those described in 

 Experiment I. Those planted in Devonshire were grown by Mr. 

 George Kerswell, of Bowhill, Exeter, in soil not previously used for 

 potatos. The character of the soil was totally different from that used 

 in Newcastle. It consisted of a stiff red clay formed from the subsoil 

 above breccia of Permian age. The climatic conditions were of course 

 very different from those of the North of England. The crop was 

 lifted in September, but was, in both cases, without a trace of the 

 blackening w^hich was present in the parent seed potatos. 



The tubers yielded by these experiments were carefully stored 

 in Newcastle during the winter, and examined again in the following 

 May. They were found quite free from the disease, so that the bruised 

 or blackened condition did not develop during storage. These experi- 

 ments collectively form a specific instance of an improvement effected 

 in unhealthy strains of varieties of potato potentially capable of yielding 

 healthy crops by effecting a change in the soil and climate. 



The disease appears in the flesh of potatos wdiich are affected, 

 as shown in figs. 20 a, 20 b, in the form of small greyish or purplish- 

 grey isolated areas. These areas occur either about the vascular 

 cylinder or between it and the periderm, so that an appearance of 

 spreading from the vascular bundles is not a constant feature. Dis- 

 coloured areas may also be present in the neighbourhood of the " eye," 

 but they seldom seem to reach the surface of the tuber. Later on the 

 areas become larger and of a darker colour. When observed wdth a 

 lens, the dark areas present a speckled appearance which is due to the 

 curious distribution of the dead and living cells — this is easily seen 

 towards the margin of the area. 



The blackening in the variety ' British Queen, ' which is illustrated 

 in figs. 20 c and 21, is of a different character. A series of potatos w^as 

 obtained showing all stages in the blackening from its first appear- 

 ance until the whole tuber became blackened. The marks appeared 

 in the first instance about the principal vascular bundles (figs. 21a, 



