GREEN VITRIOL. 173 



cause of the chlorosis, green vitriol has a very intense ameliorative 

 action and must be used in large doses. It acts on the soil by de- 

 stroying the soluble carbonate of lime and on the plant by revivifying 

 the juices and imparting to them new vigour, for the excess of carbonate 

 of lime exhausts the acid juices of the root which then cease to act. 

 It follows from Vernet's experiments that the use of green vitriol in 

 5 per cent solution with 5 per cent of sulphuric acid gives still better 

 results ; this acid decomposes the carbonate of lime and enables the 

 green vitriol to come in contact with the roots as such. Chlorosis 

 was in this way made to disappear in soils containing 19-25 per cent 

 of carbonate of lime. As to the form under which the iron ought to 

 be applied to the roots it is not definitely settled, neither do we know 

 what salt of iron is most easily assimilated by plants and under what 

 form the iron is conveyed the most easily from cell to cell. Ferrous 

 salts [of which green vitriol is one] are always, it is supposed, converted 

 into ferric salts in contact with the oxygen of the air in the soil. 

 However, many facts appear to contradict this opinion ; the most differ- 

 ent ferrous and ferric salts are capable of remedying the pathological 

 condition produced by a deficiency of iron. These salts spread by 

 copious spraying on the roots act before the ferrous salts (green vitriol, 

 etc.) can have had the time to be converted into ferric salts. If the 

 ferric salts are more active on the other hand, the ferrous salts render 

 the same service in a longer time. It must be ioaentioned that green 

 vitriol ferrous sulphate must be used in a much more dilute condition 

 than ferric sulphate. The form most favourable for artificial cultures- 

 is the phosphate of iron which the roots assimilate after rendering it 

 soluble. The following observation speaks in favour of the absorption 

 of iron under the form of ferrous salts : plants which live in marshes, 

 rich in green vitriol, possess great accumulations of iron as ferric 

 oxide in certain of their organs. {Trapa natans contains in its ash 

 68-6 per cent of ferric oxide.) These deposits cannot be otherwise 

 explained than by the precipitation by oxygen of soluble ferrous salts 

 beiug conveyed through the plant and so converted into insoluble ferric 

 salts. x\ccording to Mokrzecki it is possible that green vitriol may be 

 absorbed by the plant, and conveyed by the sap. The rapid and 

 radical cure of chlorosis by injection into the trunk of dilute solutions 

 of green vitriol which in no way affect the good working of the circula- 

 tion is a convincing proof. 



It follows, therefore, that iron may be supplied to the plant under 

 any form, and that ferric salts as well as ferrous, organic and inorganic 

 salts of iron are capable of curing chlorosis. (Gris has shown that the 

 sulphate, tartrate, malate, and acetate of iron in the dose of 0'5 per 

 cent when they are used in sprayings on the leaf produce an analogous 

 effect.) It must be admitted, in fact, that the roots can convert the 

 iron into a compound fit to circulate through the oi-gans of the plant, 

 and to produce the remarkable physiological effects described above. 

 If a certain dose be exceeded the iron becomes injurious, if given in 

 excess it is mortal. Different plants behave very differently with the 

 same dose of iron. Whilst certain plants suffer with a dose of 0*05 

 per cent of green vitriol in an artificial culture medium, trees may sup- 



