704 FUNGI 



Next, thoroughly slake the requisite amount of newly-burnt 

 quicklime in another vessel, keeping it well stirred during the 

 slaking process. When quite cold, stir the lime-water again 

 and filter it through coarse sacking into the vessel containing 

 the copper sulphate, and make up the bulk to loo gallons by 

 adding more water if necessary. 



As copper sulphate by itself is. injurious to plants, it is im- 

 portant that none of it should exist in a free state in the liquid 

 after its preparation, which is sometimes the case when old 

 quicklime is used. If a little of the mixture gives a brown or 

 chocolate colour when tested with potassium ferrocyanide solu- 

 tion, more fresh lime-mixture should be added. 



Although an excess of lime is not injurious to the plants in 

 any way, yet neutral solutions are found to adhere to the leaves 

 much better than either basic or acid mixtures. When a 

 great excess of lime is used the resulting mixture is almost 

 valueless. 



As the mixture has little practical effect on the disease when 

 once established in a crop, it is very necessary to spray before the 

 actual appearance of the ' blight,' and in wet seasons the applica- 

 tion should be repeated at intervals of two or three weeks, as 

 occasion may suggest. 



' Bordeaux mixture,' although not a very powerful fungicide, 

 hinders the germination and growth of the spores, and thus 

 prevents the spread of the disease. 



Besides acting directly as a check on the fungus, it has a 

 markedly beneficial stimulating effect on the potato plant. The 

 leaves of the latter when sprayed become firmer, transpire more, 

 and remain green, and carry on their work longer, than those of 

 plants which are unsprayed. Similar extraordinary reaction to 

 ' Bordeaux mixture ' is observable in the vine, pear and other 

 plants. In the case of the potato, the increased activity of the 

 tissues of the leaves, and the longer time which they continue 

 their work after spraying, results in a greater manufacture of 



