M INJURIOUS INSECTS AND FUNGI. [Juue 1895. 



Potato Disea.se {Phytophthora infestans) in the Tubers. 



p 



A section of infected tuber — x 150. 



The dark spots show the starch grannies and cell ivalls brown with disease. The 

 plant, or mycelinvi, is shown running betiveen the starch granules and the cell 

 walls, and sending up branches bearing conidia o>' ,'sporcs. 



It has been thought by some observers that a new disease has 

 been discovered m potato tubers, as many specimens examined 

 in the early spring of the last two or three years on being 

 cut through exhibited brown spots permeating them. In most 

 cases these spots were small and distinct. Upon exposure to the 

 air they became confluent after some time, and the whole of 

 the cut pieces ultimately turned to a brown colour. The 

 greater number of the tubers in which brown spots were found 

 displayed no outwardly visible traces of disease, particularly in 

 the early spring. In fact, it was necessary to cut many tubers 

 open in order to obtain specimens. Later on in the season, 



