lo Jan., 191--] Vhie Diseases in France 



grapes with a mixture of lime aiul bluestone. Grapfc:.s so treated, being 

 looked upon as poisonous, were left severely alone. \\'hen Downy Mildew, 

 iv.-centl\- introduced from America, commenced to ra\age the vineyards, it 

 was noticed how free from mildew were these poi.sciied outer rows. The- 

 general adoption of the copper lime spray immediately followed, and even 

 now it is the most widely used of all sprays, though several other com- 

 pounds tend to supersede it in certain quarters. 



The hydrated oxide of copper which is formed when iinir is added to 

 a copper sulphate solution* is the active agent in Bordeau.x mixture ; though 

 only slightly soluble in w\at!er, it is sufficiently so to render each drop of rain 

 or dew coming in contact with it unfit for spore germination. Its ^•ery 

 slight solubilitv. in fact, causes its influence to be more lasting, since it is 

 only entireh washed oft" by ver\ hea\'y rain. This brings us to one of the 

 most important points in connexion with copper compounds, viz.. their 

 power of adherence. It is mainly because some of the more recent sprays 

 possess it in a high degree that they tend to displace the original Bordeaux. 

 Even with this, however, adherence varies considerably according to the 

 procedure followed in its preparation, as will be seen later. 



^^'hate\■er 1)- the spraving compound used, the following are the most 

 important points to be considered in order that the best results may be 

 obtained : — 



1.- Even distribution of spraying material. 



2. Sufficient, but not excessive, solubility. 



3. Adherence, so that frequent repetition of spraying may be 



obviated. 



4. Convenience of preparation. 



The first of these is; no doubt, largely dependent on the spray pmnp- 

 employed. It cannot be too emphatically sfated that satisfactory results- 

 are not to be expected from a faulty pump. Protection cannot be com- 

 plete unless distribution is so thorough that no dew drop, however small, 

 can escape contact with some of the spray material. The fulility of throw- 

 ing a few large drops every here and there, leaving large spaces of leaf 

 surface untouched, and consequently, so many open doors for the entry of 

 the fungus parasite, is ol)\-ious. Such a course is absolutely incompatible 

 with the essentially preventi\e nature of the treatment. The subject of the 

 present article, however, is .spraying mixtures, not spray pumps, and the 

 composition of the former exercises a greater influence on the facility for 

 even distribution than might, at first sight, be imagined. 



Wetting Power of Spraying Mixtures. 



This is a question which has quite recently recei\-ed a good deal of atten- 

 tion in France. The lower the surface tension of a liquid, the smaller the 

 drops which it can form, and consequently the greater its wetting power. 

 It is for this reason that the wett'ing power of alcohol is much greater 

 than that of water. 



By the addition of certain substances it is possible to reduce the surface- 

 tension of the spraving liquid and consequently its wetting power, with 

 the result that the facilitv for even and thorough distribution is consider- 

 ablv increased. Soap is one of the substances used for this purpose, but 

 it presents the drawback of combining with the copper hydrate and modi- 

 fving the composition of the mixture, thus necessitating alteration in the 



* Aoeordiiv to Pickerin<;- (£?pwfH{/i Report of the Woburn Etperimental Fruit Farm) the active agent 

 would be a bi^-ic sulphate, and not hydroxide. Whetlier this view be correct or not is of little consec|uence,. 

 so far as its mode of action is concerned. 



