No. 4.] FRUIT GROWING. 161 



Various forms and compounds of copper have been and 

 are in use. The sulphate, known both as bluestone and blue 

 vitriol, has been employed, but at any strength of solution 

 recommended has been found destructive to the foliage. In 

 order to overcome this objection, it has been combined with 

 lime, which is of itself a weak fungicide, and this combination 

 is now known as the Bordeaux mixture. 



This seems to me to be a very unscientific preparation for 

 the purpose designed. Both substances, when in solution 

 separately, are undoubtedly fungicidal in their action, but 

 when combined they form by a double decomposition a 

 sulphate of lime, which is simply gypsum or plaster, and 

 the oxide of copper, an entirely insoluble substance. Either 

 one has destroyed the nature of the other, and rendered it 

 for our purpose almost completely inert. Six pounds of 

 sulphate of copper are directed to be combined with four 

 pounds of lime, the latter being in excess, as it should be ; 

 and this amount, used with twenty-two or twenty-five gallons 

 of water, is to be sprayed upon the foliage. A theory of its 

 action is that its presence upon the leaf by preemption 

 mechanically prevents the fungous spores from fixing them- 

 selves upon the same spot, and there developing. I have 

 no doubt that this idea is in part correct ; but, in order to be 

 fully protective, the substance must necessarily be applied to 

 the entire surface of every leaf. I have seen mildew develop 

 freely upon grapes completely surrounded within three to 

 five inches by a thick spray of Bordeaux mixture that had 

 been applied some weeks before, and that the rains had not 

 washed off. Another theory which looks more reasonable is, 

 that, as sprayed upon the leaves, the substance acts as a 

 store-house of oxide of copper, which is very slowly soluble 

 by reason of the small amounts of carbonic acid and carbonate 

 of ammonia found in rain-water, and so the copper becomes 

 active in exceedingly minute quantities. 



Another combination, known as Eau Celeste, or blue 

 water, is one in which the sulphate of copper in solution is 

 treated by adding liquid ammonia. The product is sulphate 

 of ammonia and oxide of copper. The ammonia, however, 

 being in excess, dissolves the oxide of copper, producing 

 the deep-blue color. This is sprayed upon the foliage, as 



