SOME DISEASES OF THE POTATO 



141 



Potatos. Perhaps no one would plant obviously diseased " sets " ; the 

 danger arises when the Potatos exhibit none of the external signs of 

 disease, but when cut just show indications of the discoloured patches 

 characteristic of the presence of the fungus. The obvious check to this 

 source of danger is to cut all Potatos used for planting, refusing those 

 suspected of being diseased. 



Winter-rot (Nectria solani, Pers.). 



One of the commonest of diseases attacking stored Potatos, but not as 

 a rule manifesting itself for some weeks after the Potatos have been piled 



Fig. 25. — Diseased Potato : Internal Spotting. (Gardeners' 1 Chronicle.) 



in a heap. It is rarely, if ever, met with on Potatos that are kept dry and 

 exposed to the air, whereas, when stored before being perfectly dry, 

 sweating takes place, and in some instances a very large percentage 

 becomes thoroughly rotten before the spring. 



The first outward indication of the disease is the appearance of 

 scattered white warts bursting through the skin of the Potato ; these, 

 when examined under the microscope, are seen to be covered with 

 a minute mould-like form of fruit once considered as an independent 

 fungus called Monosporium. At a later stage the same warts change to 

 a pale rose-pink colour and a second form of fruit appears, the so-called 

 Fusarium solani. The spores of the Fusarium on germination yield 

 a third type of spore, produced in a ball-like mass of gelatine, which in 

 turn was at one time supposed to be an independent fungus called 



