Marcli 1896.] 



INJURIOUS INSECTS AND FUNGI. 



439 



these are not peritliecia, nor corps miliares, but special organs 

 to enable the filaments of the fungus to penetrate into its host. 



The mycelium is at first upon the outer surface of the potato, 

 but after a time it penetrates into the interior of the tuber, and 

 then spreads rapidly. 



Fig. 3. 



A, B, C, D, E, F, the six angles of a single cell showing mycelium of Rhizoctonia, 

 Dotted lines, starch ^rrains. 



The mycelium is shown in the above figure. Its peculiar 

 variation in size and its broad inflated joints, with here and 

 there filaments of a much smaller size, will be noticed. The 

 mycelium is colourless in its broader parts, but the smaller 

 threads or filaments have a slightly brown hue. 



It was observed that there w^ere black spots throughout many 

 infected tubers, though the actual rotting had been arrested. 



Infection was discovered to be communicable by infected 

 tubers to sound ones near them in clamps or stores. A dozen 

 sound tubers were placed close to one infected, and, in three 

 weeks, eight were similarly infected. Further experiments are 

 being made in this direction. 



Where potatoes show signs of infection by this fungus the 

 store or clamp should be closely picked over, and all infected 

 tubers taken out and destroyed at once. Great care must be 

 taken not to plant infected potatoes. So far as can be ascer- 

 tained supertuberated potatoes solely, or at least mainly, have 

 been attacked, and supertuberated seed should not, under any 

 circumstances, be planted if sound strong plants are desired. 



In France lime has been found valuable in checking the spread 

 of the allied fungus which attacks lucerne. 



