14 INSECTICIDES, FUNGICIDES, AND WEED KILLERS. 



ment has been deferred and the disease has assumed a great extension, 

 it is well to remove before spraying the parts of the plant most seriously 

 attacked and to burn them ; that is a surgical complement to the 

 chemical treatment which may be of great service and which must not 

 be neglected if one be anxious to suppress the disease. It is well to 

 say that neglect of one factor may compromise the results of the 

 treatment by liquids and rob the experimental effort of any beneficial 

 result. 



I Internal Treatment. — From analogy, with the treatment of 

 human diseases, attempts have been made to introduce into the sap 

 of the plant toxic elements, intended to be carried through the plant, 

 and to destroy the mycelium of fungi which have invaded it, or to 

 kill xylophagic insects and those which suck the sap. The experi- 

 ments of Laffitte and Henneguy have shown that a substance 

 dissolved in water, absorbed by the roots, may ascend to the leaves 

 and reach the extremities of the tree if it does not form insoluble 

 compounds with the constituent elements of the sap ; however, the 

 greater number of salts yield with the plasma insoluble derivatives, 

 which prevent their entrainment by the sap towards the part of the 

 plant attacked by the parasites. Numerous experiments have been 

 made in this direction to combat the phylloxera. The method used, 

 it must be confessed with mediocre success, consisted in making a 

 hole in the vine stock from above downwards by a gimlet, and in 

 introducing therein the chemical agents such as calomel, camphor, 

 potassium sulphide. These were the first experiments carried out 

 under very bad conditions, nevertheless carbolic acid, used by Green 

 against lice, prussic acid against bugs, have given appreciable results. 

 The first fortunate results were obtained by Mokretzki with injections 

 of a dilute solution of sulphate of iron, and nutritive elements which 

 he injected into the sap to cure chlorosis. These were crowned with 

 complete success. But they must be executed in such a way that 

 the air cannot penetrate into the wound, and a slight pressure is 

 required to enable the liquid to enter into direct contact with the sap 

 of the plant. However, when Mokretzki tried sulphate of copper under 

 the same conditions, his experiments were a failure. It is possible, 

 however, that oi'ganic salts of copper soluble in the sap may behave 

 as indifferent salts, especially if used in small doses, and produce the 

 satisfactory eifects on the health of the tree given by dilute solutions 

 of sulphate of iron, and by sprinkling the soil with sulphate of copper. 

 Metals are capable of forming organic salts, which no longer precipitate 

 albumen, and, injected into the sap, may behave in quite a different 

 manner from the corresponding inorganic salts. These organic salts 

 have found multiple applications in human therapeutics, and it is to be 

 supposed that their use will extend in the domain of vegetable thera- 

 peutics. The internal treatment discovered by Mokretzki will 

 perforce extend further when it has been determined under what form 

 poisons can be incorporated with the sap, and especially in what 

 degree of concentration they should be used. These remedies will 

 form a powerful instrument against all sucker-lice, and will be capable 

 of arresting the internal evolution of the mycelium of parasitic fungi. 



