191 i.J Summary of Agricultural Experiments. 421 



Up to the present, the organism has not been found on any plant 

 ether than the potato. 



Lime-Sulphur Wash (Jour. South-Eastern Agric. Coll., Wye, No. 19, 

 1910). — These investigations were undertaken by Mr. W. B. Burgess 

 with a view to discovering (i) the best proportions of lime and sulphur 

 for making the wash, and (2) the chemical changes which the wash 

 undergoes when exposed to the air under conditions similar to those 

 which obtain when the wash is used as a summer spray. The wash 

 was considered only as a fungicide for use on the leaf in the summer. 



The self-boiled lime-sulphur wash is usually recommended for 

 summer use as it contains less sulphur in solution than one boiled 

 over a fire, and is therefore less likely to injure the foliage. It is 

 pointed out, however, that boiled washes can be diluted till they contain 

 the same amount of sulphur as self-boiled, and a much larger volume 

 is thus obtained from the Same amount of sulphur. 



The aim is stated to be to get the greatest possible quantity of 

 sulphur into solution with the least possible quantity of lime. With 

 this object small quantities of wash were made with five different 

 proportions of the ingredients, ranging from 100 lb. lime, 100 lb. 

 sulphur, and 100 gallons water, to 100 lb. lime, 300 lb. sulphur, and 

 100 gallons water, and analyses of each were made. The results 

 obtained were insufficient for definite conclusions, but as far as could 

 be judged the proportion of sulphur to lime should not exceed 2:1, 

 and the most satisfactory formula appeared to be either 150 lb. or 

 200 lb. sulphur to 100 lb. of lime and 100 gallons of water. A wash 

 with 200 lb. sulphur was made under practical conditions with ordinary 

 commercial materials, and contained in solution 1844 of sulphur 

 and 84 lb. of lime. 



The changes in the fluid after spraying were investigated by 

 exposing it in a thin layer on glass plates and examining the changes 

 in chemical composition produced. Mr. Burgess concludes that lime- 

 sulphur wash as a summer fungicide acts in two distinct ways — (1) 

 as a contact spray, the polysulphides in the wash acting in a similar 

 way to liver of sulphur; (2) as a protective coating to the leaves, due 

 to the thin layer of sulphur in a fine state of division deposited from 

 the thiosulphates and polysulphides by decomposition. 



This sulphur would be much more efficient than flowers of sulphur 

 for two reasons : (a) the former adheres very closely to the leaves, 

 in fact, cannot be removed by the most drastic washing; thus a very 

 great drawback in the use of flowers of sulphur is overcome, (b)^ 

 Owing to its fine state of division, the deposited sulphur would oxidise 

 more quickly than flowers of sulphur, and thus prove a more powerful 

 fungicide, as its action probably depends on the formation of the 

 sulphur dioxide. 



It is probable that the chief value of lime sulphur wash lies in 

 its use as a means of applying free sulphur to leaves. 



As to the question of injury, the polysulphides are the most likely 

 \ to damage the sprayed plant, as liver of sulphur where used too strong 

 is known to cause severe leaf scorching. However, these compounds 

 have been shown above to be very rapidly decomposed, so their injurious 

 action would not be very prolonged. 



Little appears to be known about the action of thiosulphates on 

 host-plants or fungi. Some preliminary trials with sodium thiosulphate 



