2 



and woody plants, as well as most of the greenhouse and garden plants, 

 field crops, and weeds. 



R. Crocorum (Pers.) DC. has been reported so far in this country 

 from only a few scattered states, on alfalfa and potato tubers. As 

 investigations continue, however, this fungus will probably be found 

 in many other localities. 



R. Solani ( C. vagum) has also been reported from Europe, Can- 

 ada, the West Indies, South America, India, and Australia, so that it 

 may be regarded as a truly cosmopolitan fungus. 



TYPES OF SYMPTOMS PRODUCED BY RHIZOCTONIA 



The symptoms produced by Rkizoctonia Solani (Corticium vagum) 

 in natural infection are largely similar when appearing on the same 

 type of host. The damping-off of seedlings and cuttings, of which 

 Rhizoctonia is the most common cause both in the cutting bench and 

 in the seed pan, is identical with the various plants, as is also the 

 rotting of a number of root crops. In most herbaceous plants, such 

 as the carnation, a stem rot is produced, the symptoms of which are 

 identical on the various hosts. On very resistant plants, however, 

 lesions only are formed ; these are apparently identical on the different 

 hosts. 



INOCULATION EXPERIMENTS 



With the view of determining the degree of biologic specialization 

 which may exist between the various cultural strains of Rhizoctonia, 

 or between strains isolated from different hosts or of different geo- 

 graphical origin, cross-inoculation experiments were conducted in- 

 volving about 3,000 cuttings, 2,000 plants, and 7,000 seedlings of vari- 

 ous kinds. With these, comparisons were made of about forty-five 

 strains of Rhizoctonia, many of which were isolated by the writer. 



When carnation cuttings were infected, the strains used, with but 

 two exceptions, whether from carnation or from other hosts, were able 

 to cause more or less loss, the mortality of the cuttings ranging in 

 either instance from to 100 percent. Again, the same strains varied 

 in virulence from one year to another, in most cases decreasing in viru- 

 lence with age. When cuttings other than carnation were used, the 

 results were the same. 



When young rooted carnation plants were inoculated, the percent- 

 age of loss was much less than with cuttings. Here, however, the 

 carnation strains seemed to be slightly more virulent than those from 

 other sources, altho there was still a great difference in the strains from 

 carnation themselves. Only one of the strains from other sources was 

 unable to attack young rooted carnation plants. 



On old carnation plants in the greenhouse which were inoculated 

 by contact, even the carnation strains did not cause a high percentage 

 of infection. However, when plants growing under these same condi- 



