178 SCIENCE AND FRUIT GROWING 



for it and the ordinary mixture consist of different substances. 

 A misconception on this point, and on similar points as regards 

 other spray-fluids, has led at various times to polemics as to the 

 relative* merits of home-made, or freshly made, spray-fluids, and 

 of preparations supplied by manufacturers. Such a controversy 

 is only raised by those who are not sufficiently versed in chemistry 

 to understand the nature of the substances under discussion. 

 Some spray-fluids must be used at once after preparation, because 

 they change their nature on being kept : ordinary Bordeaux 

 and Burgundy mixtures are cases in point ; others which do not 

 change on being kept such as the pure basic sulphates of 

 copper need not be used at once, and are certainly made much 

 better by the manufacturer, who has special chemical knowledge, 

 special appliances at his disposal, and extended experience, than 

 by the fruit-grower, who has none of these advantages. 



Determinations of the relative efficiency of Bordeaux paste 

 and of ordinary Bordeaux mixture, showed that considerable 

 variation in the ratio 12 : i must be expected according to the 

 circumstances of the case : on the one hand, experiments based 

 on the scorching action on the foliage of fruit trees which, as 

 will be shown below, is a good index of fungicidal activity 

 placed the ratio higher, namely, at about 20 : i (XI, 155) ; 

 whereas experiments carried out during several seasons on 

 potato disease, placed it considerably lower, namely, at about 

 5 to i (XIV, 7). There can be no doubt but that the ratio 

 must necessarily vary according to the nature of the disease to 

 be dealt with, and of that of the host plant attacked, for the 

 actual efficiency of a fungicide must depend, not only on the 

 potency of its fungicidal properties, but on the extent to which 

 it adheres to the plant to form a coating which will protect it 

 from further fungus attacks. Where a rapid action is required, 

 the pure basic sulphates would have the advantage; where a 

 slower action is sufficient, or where the retention of a deposit on 

 the leaves for some considerable time is necessary, the advantage 

 would often lie with Bordeaux mixture, not because it is more 

 adhesive than the paste, but because the actual amount of copper 

 applied is generally greater when using the mixture than when 

 using the paste. The nature of the climate and of the season 

 would also affect the relative efficiency of these, or any materials ; 

 the one which formed the smaller deposit on the leaves being 

 likely to suffer most by persistent rain. 



In the advocacy of Burgundy mixture during the last two 

 years, it has been repeatedly stated the Bordeaux paste is less 



