428 Scientific Proceedings, Royal Dublin Society. 



any doubt that the soil of the bad field was the more acid. Using brom 

 thymol blue and the Clark and Lubs standard buffer solutions, which are at 

 pH 0'2 intervals, it was seen that No. 1 was at pH 6'6, and No. 2 at pH 6-7, 

 or slightly more, not up to 6'8. The difference appeared somewhat less with 

 brom cresol purple. The actual numerical concentrations of hydrogen ion 

 are respectively Ch 0'25 and 0'20 x 10"° gram per litre. 



It would be of interest to study a lai'ge number of samples, and it is 

 hoped that this may draw attention to the value of the method, since, once 

 the standards are prepared, it is very rapid, and comparisons can be made 

 even without standards. Neutrality at 16° C. is at pH 7'1, and it is pro- 

 bably safe to conclude that a soil giving pH 6'9 or V'O will not be liable to 

 have its turnip crop attacked, unless possibly when subjected to heavy 

 infection through manure from animals fed on diseased turnips. It may be 

 mentioned that cabbage as well as turnips failed completely on the No. 1 

 soil, though basic slag was used with both in successive years. This soil 

 will grow nothing if touched in wet weather ; a crop of mangolds was lost 

 in trying to work it when wet. It gets sticky and then hardens, when 

 nothing will grow. It seems that the texture of this clay soil would also 

 be improved by liming, as the colloidal particles would be clumped thereby. 



It would be of interest to make a biochemical examination of diseased 

 and healthy plants to try to ascertain how it comes about that a deficiency 

 in calcium salts renders the plant more susceptible. Possibly the effect is, 

 in part at least, upon the fungus, which refuses to grow in a neutral or 

 slightly alkaline medium. This statement, quoted from Hall (1910), is based 

 on work done prior to the introduction of the present methods of determining 

 hydrogen ion concentrations, so it would be of interest to ascertain the limits 

 between which the fungus can be grown. 



No direct proof has been given that the pathogen was present in the No. 2 

 field, and the conclusion put forward has been criticized on this score. In 

 view of Hall's work, however, it seems to the writer that there is at least a 

 reasonable degree of probability in favour of the presence of the pathogen, 

 and further work will show to what extent the pH limits given here must be 

 modified. 



Summary. 



One of two adjacent fields of similar clay soil was found to be badly infested 

 with, and the other free from finger and toe disease in the turnip crop. It was 

 found that they contained, respectively, 017 and 0'40 per cent, of calcium, 

 calculated as oxide. The hydrogen ion concentration of the samples was 

 pH 6-6 and pH 6-7, or slightly over, respectively, as determined colorimetri- 

 cally, or, stated otherwise, C^ 0-25 and 0'20 x 10"= grams per litre respectively. 



