12H 



MnRPH(II.Oi:Y AM' I'AHASITISM OK HIIIZOCTONIA. 



lirowii ;it the point of infocfioii and muncrous l)l;ulc sclcrotia arc 

 fonnctl. If tlic fjrouiul nut were lirst wounded, the percentafie 

 of deaths reaehed as hi^h as fifty : tliis ])hint also seemed peeuhaily 

 susceptil)le to attack at the growing point. 



E.rpniwciil IV. — (!Rf»rxn ntt (Pi'sa .seed). 



Coic ;>m. -The svmptoins of attack in tiiis ca.se are the same 

 as tlio.se already described for the ground mit. and tlie fungus also 

 reseml)les that of the other three hosts (PI. IX. Fig. 1). Inocula- 

 tions upon the cow ])ea produce abundant sclerotia (PI. 11. Fig. 3) : 

 as in the gnmnil nut, the growing point seems peculiarly Hable to 

 infection. In the early stages of infection a red brown discolora- 

 tion appears upon the stem and slowly spreads, the stem ultimately 

 becomes flaccid and collapses. Sclerotia are formed abundantly. 

 A portion of a diseased stem was incubated and gave a vigorous 

 growth of Rhizoctonia. Infections from agar cultures on uiiwouiuhd 

 plants gave an average mortality of oO"„ : if the plants had l)een pre- 

 viously wounded at the point of infection the mortality sometimes 

 reached ae high as 80° „ of the infections. In one pot the plants 

 were infected with a piece of a diseased plant from another pot, and 

 it was noticeable that in this case the virulence of the fungus seemed 

 to be less than in the previous experiments, only one infection out of 

 six proving fatah 



