1905.] Diseased "Evergood" Potatoes. 



295 



of each of the above-named fungi, every attempt— amounting 

 to some hundreds in all — to produce the disease artificially by 

 infection, completely failed, thus proving that the fungi present 

 were only secondary factors in relation to the disease, and that 

 the true cause must be searched for along other lines. 



Plots in the Jodrell Laboratory garden at Kew were planted 

 with potatoes received from Scotland, Yorkshire, and Kent 

 respectively. Other potatoes from each source were planted, in 

 plots which, along with the soil and manure used, were sterilised 

 by steam. 



The young tubers were first examined when about the size 



DISEASED "EVERGOOD" POTATO. 



of a marble, and the true cause of the disease was at once 

 revealed. 



The skin or periderm of a potato tuber is provided with a 

 large number of breathing pores or lenticels, which in all 

 varieties of potato examined, other than " Evergood," are barely 

 visible to the naked eye. In the last-named variety, however, 

 the lenticels are very conspicuous, and project considerably 

 beyond the general surface of the tuber, so much so that when 

 a young tuber that has been carefully dug up is held between 

 the eye and the light, the surface presents a minutely velvety 

 appearance. This appearance is due to the presence of little 

 groups of dead cells that are constantly being pushed outwards 

 by the long continued division and growth of the living cells 



