i9o8.] 



Hollow Potatoes. 



287 



During the past autumn some diseased potatoes were 

 submitted to Kew for investigation. The potatoes were well 

 grown and externally showed no trace of 

 Hollow Potatoes.* injury or disease, but when cut open 

 were found to be hollow, an external 

 shell, varying from a quarter to half an inch in thickness, 

 remaining intact. 



In some examples the cavity was quite empty, dry, and 

 lined with a shrivelled mass, suggesting the previous presence 

 of some semifluid substance that had contracted and dried up. 

 In other cases the cavity was more or less filled with a glairy, 

 unpleasant smelling pulp, which on microscopic examination 

 was found to be teeming with nematodes or eelworms. 



A series of sections revealed the fact that the nematodes 

 effected an entrance into the tuber through the original point 

 of attachment to its branch. Having once gained an entrance 

 the nematodes gradually used up the substance of the tuber, 

 working from the centre outwards until their progress was 

 checked by the vascular zone which lies at some distance 

 within the periphery. 



This zone appeared in every instance to have acted as a 

 perfect barrier to the further extension of the eelworms, hence 

 the tissue lying between the vascular ring and the periphery 

 of the tuber remained uninjured. 



The nematode appeared to be Aphelenchus pyri, Bastian, 

 a species originally found in decaying pears. Its presence in 

 potato tubers, notwithstanding the amount of injury effected, 

 does not necessarily prove the nematode to be a true parasite ; 

 it is at most a wound-parasite, gaining an entrance into the 

 tuber through the minute opening formed by the decay of the 

 tissue enclosed by the vascular ring at the point of its 

 entrance into the tuber. 



Two tubers infected at the point indicated above, by 

 covering the scar with slime containing eelworms obtained 

 from a diseased tuber, were placed under a bell-jar, and kept 

 in the dark at an average temperature of 65 0 F. After ten 

 days one of the tubers was cut open and revealed a cavity 

 about one inch in diameter filled with slime containing myriads 

 of eelworms. The second tuber was allowed to remain for a 



* Kew Bulletin^ No. 3, 1908. 



