J. V. Eyrk, E. 8. Salmon and L. K. Wormald 303 



present in Solution II, and eight times that contained in Solution I. 

 By contrasting the behaviour of these it has been found that they all 

 have apparently the same fungicidal value. Again, Solution IV contains 

 less than half the sulphide sulphur contained in Solution III, and less 

 total sulphur, yet Solution IV behaves more powerfully as a fungicide. 

 The fact that this solution contains three times as much polysulphide 

 sulphur as is present in Solution III supports our earlier conclusion 

 that the proportion of polysulphide sulphur present is the important 

 factor determining the value of a sulphide spray fluid. 



Further experiments have been made with colourless ammonium 

 hydrosulphide and these again point to the inefiicacy of the sulphide 

 form of sulphur. For example, a colourless ammonium hydrosulphide 

 solution, when diluted so as to contain 3-12 % of sulphide sulphur, was 

 sprayed upon mildewed leaves and, on similarly mildewed leaves at 

 the same nodes, a diluted yellow ammonium sulphide solution was 

 sprayed which contained only 0-038 % sulphide sulphur. The latter 

 solution, however, proved to be fungicidal, whereas the colourless 

 ammonium hydrosulphide solution, containing rather more than eighty 

 times more sulphide sulphur, altliough severely checking the fungus 

 for a time, was not fungicidal. 



As experience was gained it became possible to make very close 

 comparisons of the behaviour of these spray fluids and in 1918 attempts 

 were made to determine whether there exists a relationship between 

 the percentage of polysulphide sulphur present and the fungicidal 

 action of such solutions. For this purpose solutions as widely different 

 as possible were needed, and on reference to Tal)le .5, it will be seen that 

 from this point of view a comparison of Solution VIII with Solution XI 

 was desirable. These solutions were therefore diluted so that each 

 contained the same amount of polysulphide sulphur in solution and 

 both these diluted fluids were sprayed upon mildewed leaves at the 

 same nodes. These solutions were used in this way at four different 

 dilutions, and in every case the fungicidal action was closely similar 

 or identical (see Table 2). In precisely the same way Solutions IX 

 and XI were used and in each case these two solutions behaved 

 similarly when compared on a polysulphide basis. Two other solutions, 

 Nos. V and VII, were diluted until each contained 0-077 % polysulphide 

 sulphur and the fungicidal actions of the diluted liquids were observed 

 to be similar. Solution XI was then diluted so as to contain 0-078 % 

 polysulphide sulphur and then compared at the same node with a 

 diluted solution of No. VII containing 0-077 % polysulphide sulphur. 



