GREEN VITRIOL. 



175 



TABLE XXII. — Showing the Streiigth of Solutionis of Blue and Green Vitriol 

 Required to Kill Spores of 



From the above table spores have not the same resistance to green vitriol. 

 Whilst some are very sensitive others ai-e very resistant, and support doses 

 poisonous to certain green plants. The quantity required to destroy some 

 of them is so great that there can be no question of their destruction on 

 the nurse plants by green vitriol, for the latter plants would be killed as 

 well as the parasites. That is why blue vitriol can never be replaced 

 by green vitriol in fighting the cryptogamic diseases of plants. When 

 the parasites can be attacked without injury to the plant, green vitriol 

 is an excellent cryptogamic ; its use in the treatment of anthracnose is 

 a striking example. Although green vitriol be less utilized in agri- 

 cultural medicine than blue vitriol, its use against the cryptogamic 

 parasites of our cultivated plants is a necessity in many cases. Where 

 its action is not sufficient to destroy the spores of the fungi by impart- 

 ing greater vigour to the plant, it enables it to contend more readily 

 against its parasites. Galloway has shown that sprayings with green 

 vitriol absolutely incapable of killing the spores of rust, nevertheless 

 almost entirely eliminated this disease from the grain crop. The same 

 applies to the Claviceps purpurea (ergot), a fungus reputed to have a very 

 great resistance to green vitriol, the ravages of which may, however, 

 be considerably diminished by spraying therewith. Each time that 

 green vitriol has been used as a manure for cultivated plants, or sprayed 

 thereon, improvement has resulted as well as a considerable diminution 

 in diseased plants. 



The Action of Green Vitriol on Insects. — Green vitriol has no 

 action on hard-skinned insects, for it is not absorbed so long as the skin 

 is intact (Parisot). The mucous membranes, on the other hand, may 

 absorb poisonous doses ; taken through the mouth iron salts are violent 

 poisons. Amongst mammals a small amount of iron salt may cause 

 death by stopping the action of the heart (Eabuteau). Ferric salts 

 are more dangerous than ferrous salts, because they coagulate the 

 soluble albumen and thus arrest the circulation of the vital liquids. 

 Ferric salts ought, therefore, to be regarded as violent poisons. The 

 action on insects does not make itself felt unless absorbed by the mouth, 

 in eating the leaves sprayed with iron salts. 



Use of Green Vitriol. — From time immemorial ferruginous 

 manures were used to improve crops. The Romans knew the good 

 effect of iron and utilized as a manure certain soils, rich in oxide of 



