180 INSECTICIDES, ErXGICIDES, AND WEED KILLERS. 



the amount of green vitriol used must be greater the richer the soil 

 is in carbonate of lime. If the normal quantities to be spread on the 

 soil of a vineyard generally vary between 300 and 1500 kilogrammes 

 per hectare (264-1320 lb. per acre), these quantities should rise to 4-8 

 metric tons (3o20-70iO lb. per acre) when the soil is highly calcareous 

 (Viala). This dose is spread in winter on the soil and buried by 

 hoeing. Vernet recommends, so as to diminish the dose of green 

 vitriol and to increase the action, the use of a 5 per cent solution 

 acidulated with 5 per cent of sulphui'ic acid. At the rate of 2 litres 

 per stock the results were perfect, and did not injure the roots. 

 Sulphuric acid by converting the carbonate of lime into sulphate of 

 lime lets the green vitriol penetrate more easily as far as the roots, 

 and prevents its conversion into insoluble carbonate of iron without 

 immediate ettect on the plant. The treatment of chlorosis by vitriol- 

 izing the roots tends to disappear because it is slower than treating the 

 aerial part of the plant with green vitriol solutions. 



2. Use of Green Vitriol on the Aerial part of the Plant. — (A) 

 As Spray. — -Eusebe Gris was the first to lind that by spraying the- 

 leaves of a chlorotic tree with a Oo per cent solution of green vitriol the 

 leaves rapidly assume a green coloration, tirst on the spots in contact 

 with the green vitriol, then over all their surface. This process gives 

 much quicker results than when the iron is absorbed by the roots, 

 but the effect is also more ephemeral, unless spraying is repeated 

 several times a year. It then forms an excellent method against 

 chlorosis. However, like blue vitriol, green vitriol in decomposing 

 liberates sulphuric acid injurious to plants and thus produces corrosions 

 and scorchings which only the simultaneous use of lime can remove. 

 The amount of green vitriol to be used in spraying must, therefore, be 

 well estimated so as not to exceed the amounts recognized as harmless. 

 Two per cent solutions burn the leaves treated (Dufour, Sagnier, and 

 Mohr). Brunet and Delacharlony found that the vine did not suffer in 

 contact with a 2 per cent solution, but they recommend not to use the 

 latter except on adult leaves. In spring a 1 per cent solution must do. 



(B) Use as a Coating. — This process is based on the absorptive 

 power of plant tissues in contact with solutions of metallic salts. 

 Eassigaier tried to make a radical cure of chlorosis of the vine by 

 introducing green vitriol in a strong dose into the sap. After pre- 

 liminary pruning in autumn at the fall of the leaf whilst there is still 

 a movement of the sap, the sections are coated with a 40 per cent solu- 

 tion of green vitriol ; a large portion of the iron is then absorbed. In 

 the spring the pruning of the vine is completed. This process has 

 given marvellous results, especially on vines growing in soils very 

 rich in lime, and it has replaced the process which consists in spread- 

 ing on the soil strong doses of green vitriol in the form of crystals. 

 But it is recofjnized that poisoning occurs with 50 per cent solutions, 

 but not with 40 or even 30 per cent solutions which produce the same 

 salutary effect. Thus Guillon recommends tlie use of 20 or 25 per 

 cent solutions for young and 30 per cent for adult vines. This method 

 which has numerous partisans has been used with the fourfold end in 

 view of (1) curing chlorosis ; (2) combating anthracnose ; (3) de- 



