49° Journal of Agricultural Research vol. xx, No. 6 



sulphuric-acid solution was added to the two dishes. The smaller dish, 

 set in the larger one, was filled to within i inch of the top, and the larger 

 dish was filled to the same height, so that about i inch of the smaller 

 dish projected out from the liquids. The frames were then replaced in 

 the smaller dishes, so that the threads were ]/ A inch from the surface of the 

 liquid. The lids of the outer dishes were then vaselined and made air- 

 tight. At the end of each 24 hours, two silk threads were cut off and 

 placed in tubes of beef bouillon to test for the viability of the organism. 

 The reason for the use of two dishes, both filled with the solution, will be 

 explained by Prof. Hottes in a forthcoming article. It is sufficient to 

 say that this method gives a very accurate vapor pressure, which in turn 

 could be translated into terms of relative humidity. For the sulphuric- 

 acid concentrations, vapor pressure, and relative humidity the tables 

 published by Stevens (14) were used. The specific gravity of all solu- 

 tions was determined with a Twadell hydrometer when the temperature 

 of the solution was 15 C. The dishes were set in the different tempera- 

 ture cases, so that they were exposed to a rather strong diffused light. 



The writer wishes to point out one difficulty that had to be overcome 

 and which caused him more or less trouble during the course of this 

 experiment. The citrus-canker organism, as has been pointed out before, 

 makes a very characteristic growth in beef bouillon. One of its character- 

 istics is to produce flakes after a certain time, depending on rapidity of 

 growth. Whenever a beef-bouillon culture of the organism which was 

 used to inoculate the threads showed any signs of flaking, no consecutive 

 results were obtained. Thus, several sets had to be discarded and re- 

 peated on this account. The reason is perfectly obvious and needs no 

 further explanation. Thus, it is imperative that strictly uniform sus- 

 pensions of the organism be used to inoculate the threads in order to 

 obtain consistent results. 



The results of the experiment given in Table XVIII clearly demonstrate 

 that there is a distinct influence between temperature and humidity on 

 the viability of the organism on the threads. At the medium humidities 

 (49 t<3 70.4 per cent) the organisms were alive for the duration of the 

 experiment at all temperatures. No organisms were viable at the end of 

 24 hours at the higher humidities (80.5 to 100 per cent) at 30 C. How- 

 ever, with each drop of 5 in the temperature more of the organisms 

 remained viable at these humidities, until at io° the organisms were 

 viable at all humidities for the duration of the experiment. The same 

 thing held true for the lower humidities. Here more or less variation 

 existed, but there is a more or less regular sequence in the increase of 

 viability at these humidities with each drop of 5 in temperature, until 

 we reach io°, where again, as is the case of the higher humidities, they 

 are viable for eight days. 



Because of the preliminary nature of this phase of the investigation 

 no explanation of these results can be made at this time, except to point 



