ROSE CANKER AND ITS CONTROL. 29 



Saprophytic Life of the Fungus. 



Early in^this investigation it was discovered that the canker pathogene 

 does not necessarily live all the time on the rose plant, but that it is also 

 a natural inhabitant of the soil. This was first proved by isolating it 

 under sterile conditions from soil 4 and 5 inches below the surface in 

 the rose beds. Then it was found that when sterilized soil is inoculated 

 the mycelium spreads rapidly through it and lives and grows normally 

 there for a long time. Since these pure cultures in soil have been used 

 rather extensively in this investigation, the method of making them is 

 described here and omitted in all future references. 



Method. — Milk bottles of 1 quart capacity were used. Thirty-three cubic 

 inches of rose soil, moisteued until muddy, was put in each bottle. The mouth of 

 the bottle was then plugged with cotton and the whole sterilized in an autoclave. 

 After it was cool it was inoculated by transferring a small bit of agar containing 

 mycelium to the surface of the soil. Soil so treated becomes entirely infested in 

 twelve to twenty-one days at ordinary room temperature. 



Longevity of Mycelium in the Soil. 

 Before undertaking control measures it was very essential to know 

 whether the fungus lives indefinitely in the soil, or whether it starves out 

 and dies when the rose plant is not present to furnish nourishment. On 

 March 27, 1917, eight milk bottles of soil were inoculated. At the end of 

 every month clods of soil were transferred from these bottles to acidified 

 agar plates. It has been found that when soil particles containing living 

 mA'celium are transferred to agar plates the mycelium begins to grow out 

 on to the agar within twenty-four hours, and in a few days produces 

 spores by which it can be definitely identified. The soil bottles were 

 kept in a dry culture room. No water was added to them, but the soil 

 is still somewhat moist at this writing. One year from the date of inocu- 

 lation every plate isolation gave pure cultures of Cylindrocladium. There 

 seems to be no doubt, then, that it will live for a year at least, and prob- 

 ably indefinitely, in the soil without the rose plant being present. 



Growth on Other Substrata. 

 The longevity of the mycelium may possibly be increased by passing 

 a part of its existence on substrata other than the living rose plant and 

 the soil. The abundant growth and production of spores on dead and 

 decaying rose twigs on the soil has previously been referred to. Dead 

 rose leaves were sterilized and inoculated with spores in moist chambers, 

 and it was found that the mycelium grows luxuriantly and produces some 

 spores on them. Pods of the honey locust and leaves of the papaw 

 tree — substrata on which the fungus was previously reported — were 

 inoculated in the same way. The fungus grew normally on both, produc- 

 ing spores in great abundance on the pods, and less abundantly on the 

 leaves. The great variety of artificial media on which it can be made to 



