BULLETIN 231] 



WALNUT CULTURE IN CALIFORNIA. 



359 



Paradox Hybrid and typical cultures were obtained from the diseased 

 nuts. Probably all species of Juglans can be made to take the disease, 

 although it has not been found in nature on either the eastern or Cali- 

 fornia black. Even the black seedlings in the nursery, where the dis- 

 ease usually appears, are free from the trouble. Blight infection occurs 

 not uncommonly on hybrids. 



Pecan seedlings were also inoculated very thoroughly to see if it 

 would be possible to produce the blight by using pure cultures of the 

 walnut organism. Only negative results were obtained. 



Desiccation. Several experiments were made to test out the effect of 

 drying or desiccation on the walnut organism. 



Methods. The general method of testing out the resistance of the 

 organism was as follows : 



First a tube of Dunham solution or other liquid medium was inocu- 

 lated from a pure culture and after a faint cloudiness, was visible usually 

 after twenty-four hours, a loopful of this growth was placed on half inch 

 cover glasses that had been sterilized in a petri dish. These were kept 

 in darkness and tested out by dropping them in tubes of sterilized liquid 

 media and if growth took place, dilution plates were poured and trans- 

 fers made from them to potato cylinders. If the characteristic, vigor- 

 ous, piled-up, yellow growth occurs here there is little doubt of its being 

 that of the walnut bacteriosis. In some of the last of our desiccation 

 work it was found to be necessary to make dilution cultures from the 

 tubes which had been inoculated with the desiccated cover glasses, in 

 order to be positive that the growth was due to that of the walnut blight 

 organism. In this work transfers were made directly to potato cylinders 

 from these inoculated tubes. The growth on potato is the most con- 

 clusive single test by which to identify this organism. 



Experiment I. November 5, 1908, 3 p. m. Sterile cover glasses were 

 inoculated with a two-millimeter loopful of a 22-hour culture made by 

 inoculating a tube of Dunham solution. These cover glasses were kept 

 in darkness at 20 C. and tested out as indicated in the following table : 



