EXPEBIMENTS WITH THE HAIRY-ROOT ORGANISM. 101 



lets themselves were not used, but the thickened bases were cut 

 out and used for pouring agar plates. In 4 da3^s the characteristic 

 gall colonies appeared. In 5 days they were of good size and looked 

 very much like the colonies obtained from apple galls. This was the 

 first time any such organism had been isolated from hairy-root. 



EXPERIMENTS TO DETERMINE AVHERE THE ORGANISM IS LOCATED. 



November 9, 1908. — In order to find out whether the organism 

 beheved by us to be the cause of the hairy-root of apple was located 

 in the main root under the point of origin of the hairy roots, or in the 

 flesh}^ small roots themselves, plates were poured from material cut 

 from these two locations. Colonies came up on those plates which 

 has been made from that portion of the main root lying under the 

 base of the hairy-root tuft, but none at all on the other plates; i. e., 

 the organism was not found in the hairy roots themselves. 



November 27, 1908.— An apple tree affected with hairy-root was 

 brought in from his Washington, D. C, plantation by Doctor Hedg- 

 cock, who challenged us to prove the presence of an organism. The 

 clustered roots were not dry and wiry, but fleshy and tender. Where 

 they joined the main root there was a broad, flat enlargement. 

 Plates v;ere poured from the fleshy roots and also from the enlarge- 

 ment at tlie base of these roots. As in the previous experiment, 

 the gall colonies appeared only on the plates poured from the thick- 

 ened base. 



February IG, 1909.— Some apple trees affected with hairy-root 

 were sent to Doctor Smitli by Doctor Whetzel, plant pathologist in 

 Cornell University, for us to prove the presence of a pathogenic 

 organism. Tlie roots A\'ere very dry and liad to be soaked before 

 they could be cut. Little knobs grew on the main root just where 

 the clustered roots came out, and these were used as material v/ith 

 which to pour agar plates. In four days the tj'-pical gall colonies were 

 up on the plates and were used to infect young ai)ple trees. 



HAIRY-ROOT ON DAISY. 



Inoculations of May 9, 1910 (Brown). 



Six terminal shoots on old slow-growing dais}^ I)lants were inocu- 

 lated witli the hairy-root organism. 



Result. — June 25, 1910: Four shoots are negative; 2 show several 

 tiny galls growing out of the inoculation pricks. These do not bear 

 any roots. The stems lower down bear large daisy gaUs. 



213 



