416 



JouriKil (if Ac/ricultiiic, Victurui. [10 July, 1917. 



of iron, 40 per cent.; copper sulphate, 20 per cent.; and sulphuric acid, 10 per 

 cent, by weight. Control rows were left. Unfortunately, the following spring was 

 not favorable for observations, as there was but little Black Spot. However, the 

 new spots which did appear were much scarcer in the rows swabbed with dilute 

 sulphuric acid. 



Laboratory tests with solutions as above are described. The sears were very 

 carefully swabbed, and, as soon as dry, the canes were placed in an incubator at 

 25 deg. C. in an atmosphere saturated with moisture. After two or three 

 days, they were examined. If the selerotium did not seem to have developed, 

 thin sections were placed in a drop of water in hanging drop culture. Under 

 these conditions development is very rapid, and, after a few hours, spores 

 formed. Trials made in spring, before the vines sprout, gave the following 

 result: — Scars treated with iron sulphate alone developed in every case, often 

 almost as fast as controls. Sometimes the filaments even seemed longer and 

 more vigorous than in the case of controls, no doubt owing to the slight acidity 

 derived from the iron sulphate. Traces of iron sulphate seem to rather favour 

 the development of certain fungi. Results were about the same with canes 

 swabbed with copper sulphate. Nearly all the sclerotia developed, the filaments 





Fig. 16. 



Surface view of a selerotium fragment taken from a ripened vine cane^ 

 a, 6, Kystes (small roundish bodies) at the surface of the selerotium, 

 which is visible at c; cane tissue broken down by the parasite is seen 

 at rf ( X 100). After Viala and Pacottet. 



appearing to be longer and more vigorous than on controls. Sulphuric acid, on 

 the contrary gave a quite different result. Sclerotia thus treated were like horn 

 in appearance; they became brittle, and whatever were the conditions under 

 which they were placed they never developed. 



Conclusions, — Iron and copper sulphate solutions are absolutely powerless to 

 kill Antbracnose sclerotia: swabbings with these salts give quite insufficient 

 results. If they have any efficacy, it can only be in spring, when the sclerotia are 

 in course of development. The cells of the outer layer are then thinner, more 

 active, and less capable of resistance; this, no doubt, explains why the later it la 

 applied the more eflicient the treatment. 



Below the layer of cells destroyed by the remedy, the unattacked fungus 

 tissues can, as shown above, produce new fructifications. This explains, perhaps. 



