1916] PARASITIC BHIZOCTONIAS IN AMERICA 341 



center of the cover, and a small tin tube about two inches long was in- 

 serted and soldered in. This hole was plugged with cotton. (See 

 Fig. 17.) A mixture of 200 grams of dry sand and 10 grams of corn 

 meal was then placed in the jars and moistened with distilled water 

 until the sand was wet thru. The jars and their contents were then 

 sterilized for one hour at twenty pounds pressure in an autoclave, after 

 which the sand was inoculated with a small piece of infected green- 

 bean plug upon which Rhizoctonia was growing luxuriantly. In about 

 a month the soil was permeated with the mycelium, and numerous 

 brown sclerotia of various sizes were formed. When smaller amounts 

 of infected soil were needed, a 250-cc. flask was used. 



No plant was listed as diseased until a pure culture of Rhizoctonia 

 had been isolated from it. Pure cultures were easily obtained by soak- 

 ing small pieces of diseased parts in 1-1000 mercuric chlorid for two 

 minutes and then placing them on green-bean agar. Rhizoctonia 

 developed rapidly, and in twenty-four to forty-eight hours would 

 spread out from the diseased parts. 



EXPERIMENTS 1 AND IA: INOCULATION OF CARNATION CUTTINGS WITH 

 VARIOUS STRAINS OF RHIZOCTONIA 



Rhizoctonia is the fungus most commonly found causing a damp- 

 ing-off of carnation cuttings in the greenhouse. To determine whether 

 any of the strains from sources other than carnation are able to attack 

 carnation cuttings with the same ease as those from carnation, the fol- 

 lowing experiment was carried out. Nine hundred carnation cuttings 

 and 28 strains were used in 1913, and 1,725 cuttings and 34 strains 

 in 1914. 



Sterilized flats (7x10 inches) were filled with sterilized sand; a 

 250-cc. soil culture of Rhizoctonia was then added to each and the 

 sand tamped down and watered. One flat was left uninoculated to 

 serve as a check. After two days, thirty carnation cuttings (White 

 Enchantress) were planted in each flat, January 2-3, 1913. The flats 

 were then placed in the moist chamber. 



The inoculated cuttings began to die in about three weeks (Jan- 

 uary 25), and continued dying until the healthy cuttings had rooted, 

 when the experiment was discontinued (February 11) (Fig. 18). The 

 results are given in Table 3. 



In most cases the cuttings inoculated with the various strains from 

 carnation showed a soft, wet, progressive rot at the callus, which 

 extended in many cases to the surface of the sand. This rot was very 

 characteristic of the attacks of the carnation strains (Fig. 12). At 

 other times the fungus attacked the cuttings just below the surface 

 of the soil, forming lesions of various sizes at the leaf bases. Myce- 

 lium and sclerotia were also formed along the stems and in practically 

 all cases between the leaves just above the soil. 



