1916] PARASITIC RHIZOCTONIAS IN AMERICA 345 



The strains from alfalfa, bean, and carrot produced symptoms simi- 

 lar to those from potato. A large number of the cuttings placed in 

 the uninoculated sand wilted, but none became diseased. 



During the spring of 1914, beginning on March 7 and ending on 

 April 7, the experiment was repeated, the only difference being that 

 a number of additional strains were used and flats containing forty- 

 eight cuttings instead of thirty. As will be seen in Table 3, the re- 

 sults were confirmatory. The marked increase in the virulence of the 

 lettuce strain may have been due in part to the influence of tempera- 

 ture both on the strain and on the cuttings. 



EXPERIMENTS 2 AND 2A; INOCULATION OF YOUNG CARNATION PLANTS 

 WITH VARIOUS STRAINS OF RHIZOCTONIA 



That the majority of strains can attack carnation cuttings was 

 shown in Experiments 1 and la, where it appeared that the virulence 

 of the strain did not depend on the host from which it was originally 

 isolated, but in some cases did depend on the length of time since the 

 culture was isolated. To determine whether rooted plants were as 

 susceptible to these various strains of Rhizoctonia as were cuttings, 

 further experiments were carried out : Experiment 2 in 1913, involv- 

 ing about 400 young plants and 24 strains; and Experiment 2a in 

 1914, in which about the same number of plants but only 13 strains 

 were used. 



Carnation cuttings (White Enchantress) which had been placed in 

 sterilized sand December 12, 1912, were planted February 12, 1913, 

 in sterilized flats (9x12 inches) containing sterilized soil, fifteen plants 

 in each flat. Plants failing to strike root were pulled out, leaving an 

 unequal number in the various flats. The flats were inoculated on 

 March 23 with 250-cc. soil cultures of Rhizoctonia, each flat with a 

 different strain. They were then placed in a case in the greenhouse 

 and left during April and May. 



Usually the carnation strains, as in the case of the cuttings (Ex- 

 periments 1 and la), produced a soft, wet rot at the surface of the soil 

 or just below. On other plants they caused small lesions of various 

 sizes along the stems, killing the plants slowly. Sclerotia and brown 

 strands of mycelium were as a rule present on plants which showed 

 lesions and on others less badly diseased. 



Only an occasional plant in the flats infected with other strains 

 than carnation developed a soft, wet rot. In the majority of cases 

 where infection took place the strains produced lesions of various sizes 

 on the stems at the surface of the soil or just below, slowly killing the 

 plants (Fio- 13). As a rule, sclerotia and mycelium were also present 

 on the stems of the infected plants. The plants in the check flat re- 

 mained healthy. 



