Strains of Rhizoctonia Solani Ki'ehn. 207 



English forms in regard to their effect on potato indicate that 

 the conditions of temperature and moistiu"e were unfavourable 

 to the growth of the fungi so that the results in the pre\-iou3 

 experiments were not as definite as they might have been. 

 Another experiment was therefore carried out in the laboratory 

 on a small scale where the above-mentioned factors could be 

 controlled. For this purpose ten small beakers (300 c.c. capacity) 

 were filled with soil and sterilised in an autoclave. Several 

 cress seeds were then sown on the surface of the soil and covered 

 with sterilised sand which would offer little resistance to the 



young seedlings. Distilled water was added to wet the soil 

 thoroughly. \Vhen the seedlings appeared above the surface 

 they were thinned out to twelve seedlings per beaker in such a 

 way that they were grouped fairly close together in the centre. 

 In contact with the seedlings in one of the beakers a piece of 

 potato on which E was growing was placed, and likewise /, 5, 

 A, B, PO and PE, were placed in seven other beakers. The 

 remaining two were kept as controls. All ten beakers were 

 grouped together and placed under a large bell-jar. In order to 

 keep the air moist inside the jar a beaker containing water at 

 about 90° C. w^as placed inside and the vapour from this con- 

 densed on the sides of the bell-jar. As in the pre\iou5 experi- 

 ments all cultures used were exactly the same age. In this case 

 subcultures were made on June 7th and used for infection on 

 June 14th. As nearly as could be judged by the eye the same 

 amount of fungus was placed in the beakers in all cases. 



With fungus E all seeds were healthy on the 5th day after 

 sowing (June 19th) ; on the 6th day several seedhngs were 

 attacked, on the 7th day all seedlings were attacked and on the 

 8th day (June 22nd) all seedhngs were d\ing. 



With fungus / all seedlings were healthy on the 7th day after 

 sowing but one was attacked on the 8th day, and on the 12th 

 day this was dead and two others were shghtly attacked. 



14—2 



