176 INSECTICIDES, FT-XGICIDES, AND WEED KILLERS. 



iron, still in use in Italy under the name of "Terra rosa ". In 

 Champagne, likewise, pyritic shales have been used in vineyards for 

 centuries. In the North of France, Picardy, Ardennes, Normandy, 

 and in Flanders, there are used for the same purpose the ashes of 

 Picardy which contain much iron pyrites. These are not only used 

 to double the yield of meadows but also to strengthen cereals. As- 

 tonished at the results obtained by the use of these ferruginous 

 manures, Eusebe Gris, Professor of Chemistry at Chatillon sur Saone, 

 tried to ascertain the cause. His experiments showed that the green 

 vitriol formed by the slow oxidation of the pyrites in the soil was the 

 active cause. As far back as 1840 he recommended green vitriol to im- 

 prove crops and to contend against chlorosis. The researches of his 

 son, Arthur Gris, and Knop enabled the function to be explained and 

 extended its use. Gradually it entered common use to contend against 

 the cryptogamic diseases of plants. Green vitriol may be used in 

 different ways ; in cultivation on the large scale it is spread as crystals, 

 or in 3-5 per cent solution, by watering carts ; it may also be sown by 

 hand as a fine powder intimately mixed with dry earth. To cure trees 

 of chlorosis and parasitic diseases, the incorporation of green vitriol in 

 the soil may be replaced by spraying on plants or even by injection 

 into the trunks of the trees. Used in that way the action of green vitriol 

 is felt much quicker than when it is al)sorbed by the roots. 



Use of Green Vitriol as a Weed= killer. — All plants being more 

 or less sensitive to the action of green vitriol, it is evident that by 

 using a determinate quantity of this salt all the plants which have 

 a less resistance can be eliminated from a given crop. Thus grain 

 crops possess a surprising resistance to this product, and it is possible 

 to destroy all the weeds in a field of grain without injuring the crop. 

 Steglich has treated different adult plants with a 20 per cent solution 

 of green vitriol and obtained the following results : Grain crops are 

 not attacked ; peas, trefoil, linseed, charlock suffer from this treatment ; 

 potatoes, beets, haricots, lupins are greatly damaged ; mustard is 

 killed. Stender confirms Steglich's i-esults. He treated cultivated 

 plants with a 15 per cent solution of green vitriol by spreading it at 

 the rate of 4 hectolitres per hectare (35"2 gallons per acre) and found 

 no damage on cereals, blue lupin, red trefoil, colza, poppy, and carrot, 

 but moderate damage on peas, flax, and serradelle (? saw wort) ; 

 finally much damage on millet, rape, white mustard, potatoes, and 

 beet. Twenty-five per cent solutions of green vitriol destroy almost 

 all weeds; however, horse-tails, comfrey, nettles, and carex resist 

 perfectly. The action of green vitriol solutions is especially deadly to 

 young plants when they have only throe to four leaves ; if the adult 

 plants resist concentrated (15-20 per cent) solutions, young plants cannot 

 stand much smaller doses. Strong solutions of green vitriol are not, 

 therefore, necessary when used rationally, and, as Dumont found, a 5 per . 

 cent solution suffices in most cases, especially when it is a case of destroy- 

 ing young mustard. The older the plant to be destroyed the stronger 

 should be the solution of green vitriol ; thus mustard in flower requires 

 a 10 per cent solution, adult mustard a 15 per cent solution. Gwallig 

 recommends for the destruction of this plant a 7-10 per cent solution. 



