644 THE POPULAR SCIENCE MONTHLY. 



known for more than a decade ; yet, thanks to the remarkable 

 series of investigations and experiments carried on by the Division 

 of Vegetable Pathology of the Department of Agriculture — at first 

 under the direction of Prof. F. Lamson-Scribner, and later that of 

 Mr. B. T. Galloway — assisted to a considerable extent by several 

 of the State experiment stations, their efficacy is already well at- 

 tested, and they are in practical use over a large territory. The 

 fungicides most commonly employed are the Bordeaux mixture, 

 a combination of copper sulphate, lime, and water ; eau celeste, a 

 combination of copper sulphate, ammonia, and water ; and various 

 solutions of carbonate of copper. These fungicides are sprayed 

 upon the plant early in the season, before the ingress of the disease- 

 producing fungus, in such a way that after the water evaporates 

 the leaves and stems will be coated with minute particles, usually 

 crystals, of a salt of copper. These tiny sentinels stand guard 

 over the plant ; when a fungus spore falls upon the leaf and sends 

 out its germinating tube, the latter comes in contact with the 

 copper crystal and is destroyed. 



The fungicide generally used for the downy mildew of grapes 

 is eau celeste. It is first applied in spring, a few days before the 

 vines blossom. One or two, and rarely three, additional applica- 

 tions are afterward made at intervals of about two weeks. In 

 1890 I made a special investigation of the results of spraying 

 against this disease in northern Ohio, visiting many of the vine- 

 yards personally and sending out numerous letters of inquiry. 

 As a result I was able to publish in the Bulletin of the Ohio Ex- 

 periment Station (Vol. Ill, page 262) the following paragraph : 



" The early part of the season of 1890 was peculiarly favorable 

 to the development of downy mildew, and consequently an excel- 

 lent opportunity was offered to test the value of eau celeste as a 

 preventive. It has stood the test in a remarkable manner, and 

 the efficiency of the preventive, when properly applied, has been 

 proved beyond question. All accounts agree in this respect, and 

 show that while the crops on the unsprayed vineyards averaged 

 from one half a ton to a ton per acre, the sprayed vineyards 

 yielded two to three tons per acre. Such results need no comment : 

 they speak for themselves." 



For many years pear trees, both in the nursery and orchard, 

 have been seriously affected by a fungous disease that causes the 

 leaves to drop during the summer prematurely, sometimes as early 

 as June or July. It also often develops upon the young pears, 

 causing a spotting and cracking of the fruit. The mycelium of 

 this fungus grows between and through the cells of the pear leaf, 

 causing circular brown spots to appear upon the surface ; these 

 spots gradually enlarge as the mycelium spreads through the 

 tissues, and, finally, the whole surface being affected, the leaf 



