FURTHl-R RnSFARCHES IN DISEASES OF PLANTS ^^\ 



years had included rcscartii in niosaic plant diseases. On August 

 24. Dr. Makoto Nishiinura, one of his students on this subject, 

 called on Smith at his laboratory. Frederick V. Rands doctoral 

 thesis, published March 2i), 1922 as bulletin 1038 of the Bureau 

 of Plant hidustry, "' Pecan rosette: its histology, cytology, and 

 relation to other chlorotic diseases," had been begun under Dr. 

 Harper's direction and completed under Smith in his laboratory. 

 November 15-17, 1920, Smith read a revision of this and com- 

 mented, " He thinks [pecan rosette] resembles the infectious 

 mosaics." Important research in mosaic diseases was being done 

 at the University of Wisconsin where Rand was also a graduate. 

 At Cornell Universit)', Michigan Agricultural College, and prob- 

 ably elsewhere, valuable studies of mosaic diseases and their 

 transmission in cucumber, bean, and other crops, were being made. 

 In the west curly top of sugar beet was being studied by Eubanks 

 Carsner and others. Carsner had studied at the University of Texas 

 under F. D. Heald and at the University of Wisconsin under Jones. 

 On a few occasions he conferred with Smith, and Smith regarded 

 him as a good and able scientist. On January 6, 1921, after an 

 interview, Smith wrote in his diary: 



He has been working for three years in California on tlie cause and 

 methods of transmission of curly top of the sugar beet and has found a 

 new kink which makes the etiology still more complex. The insect which 

 transmits it from beet to beet transmits it also to Erodium but if fed on 

 Chenopod'ann murale the second generation of the insect will not transmit 

 it to beets if transferred directly, but if first fed on Erodium and then 

 transferred to sugar beet will do so. He has done it over three times, he 

 says, in insect proof cages! I am to give him letters to Dr. H. Noguchi, 

 McCoy, Hitchens and Theobald Smith. 



During these years, very little was known of variant strains of 

 viruses in plant diseases, and still less of the origin and nature 

 of variant strains. In 1924 Carsner and C. F. Stalil published in 

 PJjytopathology " on " The relation of Chenopodium murale to 

 curly top of the sugar beet," and announced that an attenuated 

 strain of curly top of beets had been obtained by passing the curly- 

 top virus through the resistant weed host, Chenopodium murale. 

 Since these years it has been shown that strains of low and strong 



70 



14: 57, 1924 (abstract). See also Carsner's study. Attenuation of the virus of 

 sugar beet curly-top, Phytopathology 15(12): 745 f., Dec. 1925. 



