^06 INSECTICIDES, FUNGICIDES, AND WEED KILLERS. 



copper is present in all plants, as it is recovered in their ash. Potatoes 

 contain 0-002S grammes per kilogramme ^ (Deschamps), haricots 

 O'002-O'Oll grammes per kilogramme ((lalippe), chicorN^ salad, 

 spinach, and clover also contain it, likevsrise the vine, the fig, and the 

 plum (Papasogli). A certain amount is found in beet (Langlois), in 

 pepper (Meissnei-), and in tobacco (Wicke). Vedrosi found 06 per 

 cent of copper oxide in oak wood, 0-02 per cent in the leaves, 0-04 

 per cent in the glands ; in hai'icots the proportion is greater, and reaches 

 0-38 per cent ; in rye 0"19 per cent ; in v^heat 0'2i per cent ; in bai'ley 

 0-12 per cent ; in oats 0-35 per cent ; in maize 0-39 per cent. Whence 

 comes this copper if it were not absorbed by the roots? This belief, 

 shared by De Candolle (1832), Francis Phillips (1882), Freytag (1882), 

 and others, has been disputed by many physiologists, who, for one 

 reason or another, have not found in plants treated with copper sul- 

 phate a ponderable amount of copper, or who have found that blue 

 vitriol was too poisonous to be entrained through the plant like nutri- 

 tive salts. Pichi, on the other hand, claims to have identified, under 

 the microscope, crystals of copper in the mesophyll of the leaves of 

 plants watered by blue vitriol, and Devaux's experiments prove that 

 copper, in an insoluble form, put in contact with the roots or the 

 leaves, is assimilated by them in infinitesimal quantities and carried 

 through the plant under the form of an organic compound, capable of 

 forming deposits in the cellular membranes. The difference of opinion 

 arises in the analytical processes which have been adopted for the de- 

 tection and estimation of copper in the sap or in the ash of plants. 

 It is wrong to try to determine in all cases the amount of copper by 

 chemical or physical methods, because they are not sensitive enough. 

 The amount of copper is often so minimum that it escapes detection 

 by the chemist. Deherain advises recourse to the extreme sensitive- 

 ness of the alga spirogyra, which is affected by the dose of 0-000001 per 

 cent of blue vitriol. Ewert found a more sure method, based on the 

 presence of diastase, that is to say, on the stoppage produced in the 

 conversion of starch in presence of diastase, by infinitesimal doses of 

 blue vitriol, a method by which 0-00000051 milligramme of blue vitriol 

 may be detected. If plants are visibly healthj'- after watering with 

 copper salts, that results from the absorption of very small quantities 

 of copper that can only be determined by these latter methods of 

 analysis. It suffices to consider the infinitesimal doses of inorganic 

 salts required to exert a stimulating effect on the human organism to 

 understand the role which copper plays in the plant. 



The question then appears in quite another light, and it is in 

 homoeopathic doses that soluble copper salts must be given to plants, 

 unless reserves of copper be formed i-ound the roots of plants and 

 on the aerial organs with strong doses of insoluble or very slightly 

 soluble compounds. Wuthrich was the first to ])oint out the analogy 

 which exists between the action of green vitriol and that of blue vitriol, 

 and that of corrosive sublimate on the spores of fungi. The physio- 

 logical effect produced on plants is likewise the same, since these three 



^ = oz. per 1000 oz. . 



